Parent-Implemented Versus Clinician-Directed Interventions for Late-Talking Toddlers: A Systematic Review of the Literature

Abstract

When providing clinical services for late talkers, determining an appropriate interventionist is a key early decision. Although researchers have noted the effectiveness of parent-implemented interventions for some populations, few have specifically addressed late talkers. Late talkers are of considerable interest to early service providers and parents due to limited evidence-based intervention components with this population and the notion that early language deficits are significant risk factors for many disorders. The present study purpose is to describe general features of current research and ascertain intervention providers’ effectiveness. A systematic literature review resulted in eight studies reporting on seven data sets (N = 175 participants). Findings indicate treatment provided by either parents or clinicians can improve late talkers’ communication skills. Parent-implemented intervention emerged as potentially more effective than clinician-directed service provision based on outcome measures of targeted skills following treatment dosage. Factors limiting generalization of these findings should be addressed in future investigations.

Keywords

birth to 3 years communication evidence-based practices intervention strategies delays/disorders language/linguistics speech–language pathologists (SLPs)

Most young children experience rapid vocabulary growth during the second year of life resulting in an “explosion” of expressive vocabulary that typically includes the onset of two-word utterances (e.g., “mommy go” or “more milk”). However, roughly 10% to 15% of 2-year-olds are identified as late talkers because they are slow to develop expressive language and to produce multiword utterances relative to their same-age peers (Rescorla, 1989). A late talker is defined as a toddler between 18 and 30 months who displays typical development across many domains (e.g., play, motor, thinking, and social skills) but has difficulty with expressive language without a causal factor such as autism spectrum disorder (ASD) or intellectual deficits (Dale, Price, Bishop, & Plomin, 2003; Paul, 1996). Early delay in expressive language acquisition is associated with potentially long-term negative outcomes in the areas of literacy development, school readiness, and communication skills beyond the preschool years (Girolametto, Wiigs, Smyth, Weitzman, & Pearce, 2001; Hammer et al., 2017; Preston et al., 2010; Roos & Ellis Weismer, 2008; Snowling, Bishop, & Stothard, 2000). As a result, late talkers are of interest to researchers. These children have all the prerequisites for spoken language, yet they do not talk or talk very little, and the related potential for negative outcomes affecting additional and vital skill sets is concerning. Early service providers and parents are often involved in selecting or delivering interventions for late talkers. They can benefit from evidence-based guidance regarding the questions of if, when, and how to appropriately intervene. Unlike older children diagnosed with specific language impairment (SLI), late talkers present a unique clinical conundrum due to the potentially transient nature of their expressive language delay (e.g., as many as 60% may eventually “catch up” to typical peers) and the limited empirically based criteria for determining the necessity and effectiveness of treatment (Law, Boyle, Harris, Harkness, & Nye, 2000). Providing the appropriate dose, approach, and interventionist may positively influence treatment efficacy. Although the focus of this article is an investigation of the existing evidence base regarding appropriate treatment provider, a brief review of intervention approaches commonly employed with late talkers will assist in evaluating the available evidence for intervention providers.

Intervention Approaches

To date, there are three common intervention approaches that have been used for late talkers: general language stimulation, focused language stimulation, and milieu teaching (Rescorla & Dale, 2013). General language stimulation involves the establishment of a rich linguistic environment that fosters opportunities for a child to hear quality adult language input, but specific language forms are not explicitly targeted (for further discussion, see Baxendale & Hesketh, 2003; Finestack & Fey, 2013; Robertson & Ellis Weismer, 1999). Focused language stimulation is similar but includes the identification of specific language targets such as specific vocabulary words or particular syntactic structures (for further discussion, see Finestack & Fey, 2013; Girolametto, Pearce, & Weitzman, 1996). Milieu teaching is a more structured approach that involves an increased use of models and prompts. During enhanced milieu teaching (EMT), adult responses are contingent on child utterances (for further discussion, see DeVeney, Cress, & Reid, 2014; Ellis, Weismer, Murray-Branch, & Miller, 1993; Kouri, 2005).

Interventionist Considerations

A major factor in intervention implementation is determining the appropriate treatment provider: either a speech–language clinician or the child’s parent/caregiver. Although parental involvement is a key factor in treatment protocols for infants and toddlers to promote skill generalization and long-term positive outcomes, the nature of involvement varies considerably across early intervention settings. Parents may be central or peripheral to treatment procedures. Wetherby and colleagues (2014) noted that even intensive clinician-implemented treatments include some aspects of parent involvement; however, “the focus is on clinician-child curricula rather than parent implementation” (p. 1085).

Clinician-Directed Therapy

Conventional practice includes direct therapeutic service delivered by a speech–language pathologist (SLP). Direct services include individual and group formats in which the SLP provides skilled intervention to the client(s) themselves. This does not include indirect or educational services provided to parents, caregivers, or educational/medical staff members of the client. Traditionally, clinician-directed services have been associated with child care centers or clinical settings. However, clinician-directed therapy may occur in the home environment or other parent-designated natural environments (e.g., child care center) when providing services to children from birth to 3 years of age, or to older individuals through home health.

In response to federal mandates and shifting professional landscapes, service delivery formats have changed in a number of clinical environments, including that of early childhood intervention. For example, the Individuals With Disabilities Education Improvement Act (IDEIA; 2004) mandated that interventions for young children with disabilities include typical and realistic learning experiences. This served to emphasize the significance of parent–child interactions, as well as parents as children’s first teachers in home-based, natural environments, giving rise to parent-implemented therapy approaches (Roberts & Kaiser, 2011).

Parent-Implemented Therapy

Parent-implemented therapy involves speech–language interventions implemented by parents/caregivers directly to the child, supported with training, coaching, and/or feedback from the SLP. When facilitating a parent-implemented therapy program, clinician-directed training may include workshops, videos, and/or manuals (Roberts & Kaiser, 2011, 2012). The parent-implemented intervention model represents an alteration in the traditional SLP role to that of adult educator, facilitator, collaborator, and/or consultant (American Speech-Language-Hearing Association [ASHA], 2008; Girolametto, Weitzman, & Earle, 2013).

Researchers and meta-analysts have noted positive outcomes regarding the effectiveness of parent-implemented interventions for other normative and clinical populations. These populations include young children with developmental delays, children diagnosed with ASD, and children at risk for language delay due to poverty (Girolametto et al., 1996; Hemmeter & Kaiser, 1994; Kaiser & Roberts, 2013; Law, Garrett, & Nye, 2004; Leffel & Suskind, 2013; McConachie & Diggle, 2007; Roberts & Kaiser, 2011; Roberts, Kaiser, Wolfe, Bryant, & Spidalieri, 2014; Subramanian, Gladfelter, & Wendt, 2011; Wetherby et al., 2014). However, previous literature reviews regarding this topic were conducted with populations representing wide age ranges, including children older than 36 months (e.g., Law et al., 2004; Roberts & Kaiser, 2011), and differential populations, such as young children with ASD (e.g., McConachie & Diggle, 2007). Few published studies were specific to late talker interventions. As a result, little is known about the effectiveness of parent-implemented treatments for late talkers. This lack of data-based literature gives early service providers and parents insufficient guidance for evidence-based clinical decision making with this unique early childhood population.

The aims of the present literature review were twofold. The first aim was to describe the general features of intervention research with late talkers to aid investigators and clinicians in the evaluation of what is currently known. The second aim was to determine the effectiveness of intervention providers for late talkers. Are both intervention provider models effective for treating late talkers? For the purpose of this review, to incorporate a variety of participant sample sizes and research designs, interventions deemed “effective” were those in which study outcome measures indicated improvement in targeted skills following treatment dosage for the majority of participants. This review also incorporates a discussion of factors limiting comparisons between parent-implemented and clinician-directed interventions for late talkers and across parent-implemented interventions. Recommendations for how these limiting factors may be addressed in future research to better inform clinical decision making are included.

Method

To systematically identify articles on parent-implemented and clinician-directed interventions for late-talking toddlers, a multistep identification process was followed (Appendix A). Following the identification process, 73 citations were retrieved and reviewed by the authors using a coding protocol (Appendix B) which resulted in eight articles meeting criteria for inclusion in this review. The majority of the 65 articles were rejected because the study did not involve child intervention (n = 23 articles). Additional factors for excluding articles included participants not meeting inclusion criteria (e.g., included target populations of children with primary disabilities beyond language delay or participant inclusion criteria were unclear; n = 13 articles) and participants not meeting the age requirements (e.g., too young; n = 9 articles). Two studies were omitted from consideration because they were not conducted in home or clinical settings. The remaining 18 studies were duplicates of the included studies.

Results

Seven data sets were reported in the identified eight studies because two studies presented data separately on the same participant sample. The seven data sets included a total of 175 children identified as late talkers by the researchers. For summative descriptions of the individual studies, see Table 1. For aggregate descriptive data across the reviewed studies, see Table 2 for participant characteristics and Table 3 for intervention components. For information addressing the quality of the research, see Table 4.

Table 1.

Parent-Implemented and/or Clinician-Directed Intervention Studies for Late Talkers.

Author(s)	Participants^a	Intervention provider(s)	Child intervention setting(s)	Intervention approach	Outcome measure(s)	Standardized measure(s) used	Results
DeVeney, Cress, and Reid (2014)	n = 3; 29.7 months (range = 25–33 months)	Clinician-directed	Home	Focused language stimulation and milieu teaching	Expressive vocabulary (target word use)	NA	Both approaches were effective for all participants and showed advantage over untreated control words; no advantage of one approach over the other
Ellis Weismer, Murray-Branch, and Miller (1993)	n = 3; 25.3 months (range = 25–26 months)	Clinician-directed	Clinic	Focused language stimulation and milieu teaching	Expressive vocabulary (target word use)	NA	One participant responded with improved performance to focused language stimulation, one to milieu teaching, and one did not respond effectively to either
Gibbard, Coglan, and MacDonald (2004)	n = 22; 24.1 months (range = 22–30 months)	Both parent-implemented and clinician-directed conditions	Home and clinic	General language stimulation	Receptive, expressive language skills; expressive vocabulary, phrase length; MLU	Reynell Developmental Language Scales; PLS-3 UK	Child participants had significantly better language skills in parent-implemented versus clinician-directed intervention on all measures except estimated expressive vocabulary
Girolametto, Pearce, and Weitzman (1996, 1997)	n = 25; 28.7 months (range = 23–33 months)	Parent-implemented	Home	Focused language stimulation (modified Hanen Program for Parents)	Expressive vocabulary (general; target word); expressive language skills; “talkativeness”; multiword utterances; parent language measures (1996); phonological diversity; accuracy (1997)	NA	Participants utilized more target words, more words overall, and exhibited larger vocabularies in intervention condition than in delayed-treatment group. Parent language input slowed, and was less complex and more focused than that of control group (1996); participants exhibited increased phonological diversity, but not accuracy in intervention condition
Roberts and Kaiser (2015)	n = 97; 30.5 months (range = 24–42 months)	Both caregiver-implemented and clinician-directed conditions	Home and clinic	EMT	Receptive and expressive language skills; receptive and expressive vocabulary; caregiver use of strategies; caregiver stress	Child: PLS-4, CDI,^b EOWPVT, PPVT Parent: Parenting Stress Index	Participants had significantly better receptive language skills in caregiver-implemented condition but not expressive language Caregiver interaction improvement was noted
Roberts, Kaiser, Wolfe, Bryant, and Spidalieri (2014)	n = 4; 30.8 months (range = 25–38 months)	Caregiver-implemented	Clinic	General language stimulation and EMT	Receptive and expressive language skills; MLU; expressive vocabulary use; caregiver use of strategies	PLS-4, EOWPVT	Three of four participants exhibited improvements across all language measures. Caregivers demonstrated greater use of language strategies after instruction
Robertson and Ellis Weismer (1999)	n = 21; 25.1 months (range = 21–30 months)	Clinician-directed	Clinic	General language stimulation	Expressive vocabulary; MLU; % intelligible utterances; socialization; parental stress	NA	Significant differences were noted across the experimental condition compared with the delayed-treatment group for all outcome measures: Increases in vocabulary, MLU, intelligible utterances, and socialization; decrease in parental stress

Note. MLU = mean length of utterance; PLS-3 UK = Preschool Language Scale–3 UK Edition; EMT = enhanced milieu teaching; CDI = Communicative Development Inventory; EOWPVT = Expressive One Word Picture Vocabulary Test; PPVT = Peabody Picture Vocabulary Test.

Sample size; age at intake in months; age range at intake in months. ^bMacArthur–Bates Communicative Development Inventories: Words and Sentences (CDI).

Table 2.

Aggregate Descriptive Data for Participant Characteristics.

Language of the home	Age	Gender	Race/ethnicity	Socioeconomic status	Receptive language skills
All reported; participants spoke English in the home and were monolingual	All reported; M = 27.7 months; median = 27.2 months; range = 21–42 months	All reported; male (n = 91; 52%), female (n = 84; 48%)	Reported in five of seven data sets (71%); Caucasian (n = 128; 73%), African American/African Canadian (n = 19; 11%), “Other” (n = 4; 2%), Asian (n = 2; ~1%)	Reported in six data sets (85%); these data were not quantifiable (e.g., reported in nominal or ordinal formats such as middle class, upper-middle class, armed forces)	Assessed in six data sets (85%); distinguished in intervention outcomes for a single data set (n = 3 participants; n = 1 with receptive language deficits) Five data sets (n = 150 participants) assessed during intake, but intervention outcomes not distinguished One data set (n = 22 participants); receptive language capacities not specifically reported

Table 3.

Aggregate Descriptive Data Across the Reviewed Studies for Intervention Components.

Intervention providers	Intervention settings	Intervention approach	Intervention focus areas measured
Three of seven data sets (42%), interventions implemented by clinicians Two data sets (28%) by parents/caregivers Two (28%) reported on both	Two data sets (28%) provided intervention at home Three (42%) in clinical setting Two (28%) in both	10 interventions reported (some studies compared two or more interventions) Three data sets included general language stimulation Three included focused language stimulation Four included milieu teaching/EMT	Child targets Expressive vocabulary (n = 5) Receptive language (n = 4) Expressive language (n = 4) “Estimated” expressive vocabulary (n = 1) Estimated phrase length (n = 1) MLU (n = 2) “Talkativeness” (n = 1) Multiword utterance (n = 1) Parent language (n = 1) Phonological diversity and accuracy (n = 1) Intelligible utterances (n = 1) Socialization (n = 1) Parent targets Caregiver use of strategies (n = 2) Caregiver stress (n = 2)

Note. EMT = enhanced milieu teaching; MLU = mean length of utterance.

Table 4.

Quality of Research per Evidence-Based Practice Guidelines.

Level 1b^a	Level 2a	Level 2b
Well-designed randomized controlled studies	Well designed, not randomized	Quasi-experimental
Four of eight studies (50%; Girolametto, Pearce, & Weitzman, 1996, 1997; Roberts & Kaiser, 2015; Robertson & Ellis Weismer, 1999)	One study (12%; Roberts et al., 2014)	Three studies (38%; DeVeney, Cress, & Reid, 2014; Ellis Weismer, Murray-Branch, & Miller, 1993; Gibbard, Coglan, & MacDonald, 2004)

Per established criteria (American Speech-Language-Hearing Association [ASHA], n.d.; Dollaghan, 2004).

General Features

Participants

The average participant was a 27-month-old Caucasian male native English speaker with expressive-only language deficits. Although all included studies indicated the language of the home (English), age, and gender, only five of the seven data sets reported race/ethnicity information and, of those, the majority of participants were Caucasian (n = 127 participants). Although six of the seven data sets included some measure of receptive language skills at intake (n = 153), only one small data set distinguished receptive language status in intervention outcomes for one participant.

Intervention components

Setting, intervention approach, and measured targeted skills were each reviewed to describe elements critical to intervention.

Setting

Most clinician-directed intervention studies were conducted in a clinical setting (n = 4 of 5 studies included), and most parent-implemented interventions were delivered in a home environment (n = 3). One clinician-directed study was conducted in the home and one parent-implemented study was conducted in a clinic.

Approach

In the seven data sets reviewed, a total of 10 interventions were reported as some studies compared two or more intervention approaches. General language stimulation was reported in three of the data sets, focused language stimulation was reported in three, and milieu teaching/EMT was reported in four. All three types of intervention were studied when implemented by parents and clinicians. Direct interventionist comparison studies included only general language stimulation and milieu teaching.

Focus areas measured

Within the 10 interventions studied, over 12 targeted skill areas were measured before and after treatment dosage. Because the majority of the data sets (n = 5) reported on more than one targeted skill, a total of 27 reports of targeted skills were identified.

Research quality

The scientific rigor and quality of each study determines the level of support it offers for evidence-based practice. Levels of evidence span from meta-analysis of randomized controlled studies (Level 1a) to expert opinion based on clinical experience (Level 4) (ASHA, n.d.; Dollaghan, 2004). The span of studies included in this review ranged from Level 1b, well-designed randomized controlled studies, to Level 2b, quasi-experimental studies that indicate limited evidence for affecting clinical practice.

Provider Effectiveness

All eight reviewed studies evidenced effective treatment outcomes. The studies indicated that both parent-implemented and clinician-directed interventions were effective for late talkers. Outcome measures varied across studies and included pre- or post-performance on standardized assessments (n = 3 studies) and progress monitoring on target skills (n = 5). Child participants across all studies demonstrated improvement in the following reported outcomes: specific target word use (n = 4 studies), expressive vocabulary (n = 4), mean length of utterance (MLU; n = 3), expressive language skills (n = 3), receptive language skills (n = 3), phrase length (n = 2), total number of words used/total number of different words used (n = 1), phonological diversity (n = 1), intelligibility (n = 1), and socialization skills (n = 1). Child participants did not indicate improved target skills in the area of accuracy of speech sound productions compared with adult word models (n = 1 study).

In studies that included parents as providers, measured parent participant outcomes were also deemed effective based on study criteria. Areas in which improvements were noted included slowed, simplified, and focused language input (n = 1 study); use of targeted strategies taught such as matched turns, expansions, and prompting (n = 2); and decreased parental stress (n = 2). Parent outcome indicators were not specified in studies reporting only clinician-directed interventions.

Through the review, two studies were identified that directly compared intervention according to provider type. Both studies (Gibbard, Coglan, & MacDonald, 2004; Roberts & Kaiser, 2015) found that parent-implemented interventions resulted in greater improvements in child outcomes. Specifically, Gibbard et al. (2004) reported significantly greater gains in the parent-implemented condition for all measured language skills except estimated expressive vocabulary. Likewise, Roberts and Kaiser (2015) found significantly better receptive language outcomes but not expressive language outcomes for the parent-implemented condition.

Discussion

The purpose of this literature review was to describe the common features of current intervention research with late talkers, investigate the effectiveness of intervention provider for late talkers, and underscore factors restricting comparisons between parent-implemented and clinician-directed interventions and across parent-implemented interventions to inform investigators and practicing clinicians about limitations in the current evidence base. The studies included in this review indicated support for intervention with late talkers, as all reported interventions were connected with improved outcomes following treatment regardless of intervention provider (parent or clinician). Although all reviewed studies demonstrated both intervention provider types (i.e., parent, clinician) to be effective, parent-implemented interventions resulted in better outcomes in the two studies that explicitly compared parent-implemented with clinician-directed services for this population. However, this was interestingly not in the targeted areas that are perhaps of most value to parents and clinicians: expressive vocabulary use and expressive language skills (Gibbard et al., 2004; Roberts & Kaiser, 2015). In addition, consensus regarding the type of target skills for which improvement was noted was not achieved: Gibbard et al. (2004) reported gains across all targeted language skills except expressive vocabulary, whereas Roberts and Kaiser (2015) noted greater improvements in receptive language skills targeted but not expressive.

Variability across a number of key factors made comparison between interventionist types difficult, namely, (a) information provided regarding participant characteristics, (b) dissociation of setting from interventionist, and (c) systematic investigations of intervention approach and, relatedly, of targeted skills for outcome measures. Variability in parent training procedures limited comparison across parent-implemented interventions and may not reflect parent training procedures utilized in current clinical practice.

Factors Limiting Comparison Between Interventionists

Participant characteristics

Although some participant and setting characteristics (e.g., gender and age) were readily reported in the literature, other descriptive variables were not consistently reported, which limits comparison across data sets. Consistent reporting of socioeconomic status (SES) and other descriptive data such as race/ethnicity would allow for more transparent documentation and lead to more efficient clinical application of research study findings.

Inconsistent reporting of children’s receptive language status at intake and following treatment dosage also limits comparison across intervention studies. Deficits in receptive language are likely associated with a child’s response to treatment, as was noted in the only data set that distinguished receptive language capabilities in intervention outcome reporting (DeVeney et al., 2014). The researchers found that individual variations to treatment were noted, and the presence of a receptive language delay was identified as a possible contributing factor. However, this data set was small (n = 3), and more research is needed to investigate the potentially influential role of receptive language ability in the effectiveness of late talker interventions. In most of the reviewed data sets (n = 5), receptive language skills were not reported separately from expressive language skills in intervention outcome reporting. Consistent reporting of such associative skills leads to a more refined evidence base regarding intervention—and interventionist—effectiveness.

Setting dissociation

While there were differences in treatment outcomes noted between clinician-directed and parent-implemented interventions, treatment setting is a potentially confounding variable when comparing these results. Separating treatment setting from interventionist is an important step in more clearly determining intervention components critical to successful treatment delivery for late talkers. Based on available research, it is difficult to detangle whether receiving services in a more casual home environment is more significant for treatment success than intervention provider. Future comparative research in this area would benefit from directly addressing the dissociation of setting and interventionist.

Intervention approaches and focus areas measured

Although parent-implemented intervention was viewed as more effective in the two studies directly comparing parent-implemented and clinician-directed treatment, there was not a direct comparison study for one type of intervention approach: focused language stimulation, indicating an area for further research. General language stimulation and milieu teaching were addressed in a direct comparison between interventionists, but there may be features specific to focused language stimulation (e.g., identification of appropriate specific vocabulary or syntactic structures to target, adherence to adult modeling without request for child utterances) that favor clinician-directed treatment delivery. More research is needed to determine the association of intervention approach with intervention provider success.

Intervention approach typically guides the focus areas measured to evaluate the effectiveness of the intervention. For instance, when implementing an approach where one or more aspects of language are specifically targeted (e.g., focused language stimulation), researchers often select outcome measures related to the structures/words targeted (e.g., target vocabulary use). In contrast, when utilizing a general language stimulation approach, targeted outcomes often include more broad-based aspects of language (e.g., receptive and expressive language skills). Many different child and parent outcome measures were reported in the eight selected studies. This is not surprising due to the inherent differences in outcome measurements and the wide variety of skills that could potentially be measured to show improvement in the developing communication skills of young children or associated communicative behavioral changes for their parents. However, agreement on target skills and corresponding measurement outcomes would enable more effective comparison across intervention approaches and providers, which serves as a direction for future research. In addition, although studies showed improved child performance on many language targets and general communication skills, in one study (Girolametto, Pearce, & Weitzman, 1997), child participants indicated improvements in one aspect of phonological improvement (phonological diversity) but not another (accuracy of speech sound productions compared with adult word models). These findings indicate inconclusive support for late talker interventions specific to phonological skills. More research is needed to establish evidence-based support for intervention with this population to improve phonological skills.

Factors Limiting Evidence Base of Parent-Implemented Intervention

Variations in parent training procedures

A major factor limiting a comparable evidence base across parent-implemented interventions is inconsistency in parent training procedures. In cases of parent-implemented interventions (n = 4 data sets), information was reported on their training. Although parent training was noted in all data sets that involved parents as interventionists, training procedures for parents were not reported in a consistently quantifiable manner across data sets (see Table 5). Training length ranged from 11 weeks to 6 months, with a mean of 14.75 months across the four studies, and included combinations of structured lectures/workshops, strategy demonstrations, role-play, coaching, and feedback on parent performance. Specific information on testing-out of training (e.g., achieving a criterion of implementation or set amount of fidelity of implementation) was not reported in any data set. Future research regarding the amount, extent, and fidelity of parent training required to achieve significant results in participant outcomes would be beneficial to provide an evidence base for informed clinical practice.

Table 5.

Parent training in parent-implemented interventions for late talkers.

Author(s)	Intervention provider(s)	Parent training
Gibbard, Coglan, and MacDonald (2004)	Both parent-implemented and clinician-directed conditions	Eleven 90-min group sessions over 6 months; structured teaching, demonstrations, and practice activities
Girolametto, Pearce, and Weitzman (1996, 1997)	Parent-implemented	Eight sessions over 11 weeks; lectures, role-plays, discussions, and individualized feedback and coaching
Roberts and Kaiser (2015)	Both caregiver-implemented and clinician-directed conditions	28 sessions over 3 months; teach-model-coach-review method
Roberts, Kaiser, Wolfe, Bryant, and Spidalieri (2014)	Caregiver-implemented	24 individualized sessions over 12 weeks; teach-model-coach-review method

Ecological validity of parent training procedures

Although some of the training procedures may be included in typical early childhood service provision (e.g., continuing education for child care center staff), it is not known whether all procedures are considered standard for early intervention, home-based SLPs. As such, study results may not reflect common practices in the field. More research is needed to determine procedures utilized in typical practice, as well as the nature and extent of parent training programs used in early childhood settings.

Research Implications

The results of this review highlight research implications that should be addressed in future studies. First, consistent reporting of participant demographic data such as SES and child receptive language status along with more readily available intervention outcome data related to receptive language skills would provide descriptive information regarding the role of unique participant characteristics and language comprehension deficits in treatment response. Second, additional studies separating setting-provider information (e.g., parents at home and clinicians in clinical setting) would help determine factors important to effective intervention. For example, some settings may be more conductive to intervention components and may influence outcomes. Third, a focus on the systemic study of intervention approaches and interventionists would benefit evidence-based practice. For instance, studies for focused language stimulation across parent-implemented and clinician-directed conditions are needed, as no studies have determined whether focused language stimulation varies across intervention provider. Fourth, agreement on target skills and measurement outcomes would allow for more direct data set comparisons. Perhaps some language and/or communication targets are more aptly addressed with parent-implemented treatment and some for which clinician-directed intervention is more efficacious. Little is known about intervention effects for phonological skills and should be addressed in future research as well. Fifth, determining the nature and extent of typical parent training procedures used in early childhood settings, and ensuring that these procedures are replicated in research methodology, would provide support for the ecological validity of this work. Finally, research in this area would benefit from elevating the evidence level by engaging in more rigorous intervention research designs overall (e.g., fewer quasi-experimental studies, more randomized controlled studies).

Limitations

A number of limitations should be noted in this systematic review. First, although the authors attempted to conduct an exhaustive review of the literature, it is possible that due to the search terms selected, and the mode of article collection (i.e., via the electronic databases), some studies on this topic were not identified. Second, initial search restrictions (e.g., published in peer-reviewed journals) may have excluded certain studies. In addition, some articles were excluded due to poor reporting of child or participant data. If the participants could not be clearly identified as meeting inclusion criteria, or the intervention conducted was not clearly specified, the study was excluded. Finally, although efforts were made to effectively compare study outcomes, differences in treatment outcome measurements (e.g., informal measures vs. standardized scores) and study sample sizes limited the authors’ ability to review the evidence through statistical comparisons such as effect size and improvement index.

Conclusion

Relatively few studies have been conducted investigating parent-implemented or clinician-directed interventions specifically for late talkers. However, despite limitations in the number of published studies, support exists for the idea that interventions provided by either parents or clinicians can effectively improve language and, for late talkers, parent-implemented intervention may be more effective than clinician-directed service provision. Much more research is needed in the area to facilitate clinical application of research findings.

Footnotes

Appendix A

Article Identification Process.

Step 1a	Search of electronic databases	Sources: Education Source, ERIC, MEDLINE, PsycINFO, and Web of Knowledge/Web of Science Goal: Identify published, peer-reviewed articles between 1990 and October 2015 Search Terms Fields: (a) “Late talkers,” “late language emergence,” “early language delay”; and (b) “intervention,” “treatment,” “therapy”
Step 1b	Manual search of ASHA journals	Sources: American Journal of Speech-Language Pathology; the Journal of Speech, Language, and Hearing Research; and Language, Speech, and Hearing Services in the Schools Goal: Same as above Search term fields: Same as above
Step 2	Review article titles and abstracts	Title and abstract review criteria: (a) Written in English; (b) used one of the following designs: experimental, quasi-experimental, or descriptive/nonexperimental group design; (c) participants included toddler/preschool children 18 to 42 months of age (mean age less than 36 months) identified as having a delay in language development not secondary to other developmental deficits; (d) intervention was provided in the home or a clinical setting (not a classroom); and (e) intervention was provided by SLP, graduate students, and/or parents.
Step 3	Review of full manuscripts	Full manuscript review criteria: See Appendix B

Note. ERIC = Education Resources Information Center; ASHA = American Speech-Language-Hearing Association; SLP = speech–language pathologist.

Appendix B

Coding Protocol for Articles Reviewed

Inclusionary and Exclusionary Criteria.
Participants	Included: 18 to 42 months of age with a mean age of 36 months or less; identified as late talking or as having a language delay, vocabulary delay, expressive language delay, or delays in language acquisition not secondary to other developmental deficits Excluded: Studies that included children with hearing loss, developmental delays, cognitive delays, autism, PDD, or other neurological disorders
Intervention setting	Included: Any treatment conducted in the home and/or clinical setting Excluded: Classroom-based intervention settings
Research strategy	Included: Experimental, nonrandomized (quasi-experimental), or nonintervention/descriptive study (including correlational and case studies) Excluded: All others
Study design	Included: Treatment–comparison group designs, single-group designs, and single-subject studies Excluded: Case studies that did not incorporate single-subject research design, in which a subject serves as his or her control, were not included
Dependent variable	Included: Studies that reported dependent measures of child participants’ receptive language, expressive language, or both Excluded: All others
Independent variable	Included: Any treatment designed to increase the expressive language abilities of the participants. Treatments were delivered by SLP, SLP graduate students, and/or parents Excluded: All others
Descriptive Criteria.
Intervention provider	Categorized as parent, clinician (i.e., SLP or SLP graduate students), or both
Characteristics of parent training	For interventions provided by parents or a combination of parents and SLPs, described parent training techniques (e.g., using a manual, audio/videotapes, supervision/consultation with a clinician, informal or formal training with a clinician, a combination of these, or other)
Level of intervention	Categorized as individual sessions, group sessions, or a combination
Duration of intervention	Described in number of weeks, sessions per week, minutes per session, and/or total number of sessions
Intervention focus areas	Categorized as acquisition of specific target words, gains in expressive vocabulary, an increase in mean length of utterance, other, or any combination of the above-listed categories
Type of treatment	Categorized as general language stimulation, focused language stimulation, milieu teaching, AAC, or other
Child participant demographics	Information reported about child participants was coded, by group, as total number of participants, number of males or females in a group, mean age in months at the start of the intervention, SES (low, high, middle), race/ethnicity (Latino/Hispanic, African American, Caucasian, Other), languages spoken by child participants (English, other), and maternal education level
Measurement design	If reported, categorized as pre- or posttesting, posttest only, pre- or posttest/follow-up, or other
Specific therapy methods	Described in narrative format
Major findings	Recorded in narrative format

Note. PDD = pervasive developmental disorder; SLP = speech–language pathologist; AAC = augmentative and alternative communication; SES = socioeconomic status.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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