Parent–child book reading across early childhood and child vocabulary in the early school years: Findings from the Longitudinal Study of Australian Children

Abstract

Vocabulary knowledge is a critical component of school readiness. The current study investigated the extent to which low levels of joint attention in infancy and parent–child book reading across early childhood increase the risk of children having poor vocabulary around the time of school entry. Relevant data from the Longitudinal Study of Australian Children were available for 2369 children (1211 boys) who had a median age of 9 months (M = 9.3 months, SD = 2.1 months) at wave 1 and a median age of 58 months (M = 58.0 months, SD = 2.5 months) at wave 3. As hypothesised, children who had low levels of joint attention at wave 1 were significantly more likely to have poor receptive vocabulary at wave 3. Furthermore, children who had low levels of parent–child book reading across early childhood were two and a half times more likely to have poor vocabulary at wave 3. These results converge with the findings of training studies and underline the importance of educating current and future parents about the pivotal roles of joint attention and parent–child book reading for children’s language development and hence their readiness for school.

Keywords

Joint attention language development language problems parent–child book reading school readiness vocabulary development

Language acquisition is a critical developmental task and forms an integral component of school readiness (Brinkman, Sayers, Goldfeld, & Kline, 2009; Janus & Offord, 2007). The importance of development in the years before school is becoming more widely recognised, in part, because school readiness is a good predictor of scholastic achievement and high school completion (e.g. Reynolds, Temple, & Ou, 2010; Romano, Babchishin, Pagani, & Kohen, 2010). Social constructivist theorists (e.g. Bruner, 1975; Vygotsky, 1981, 1987) have long recognised that parent–child interaction facilitates early language development. Similarly, bioecological theorists such as Bronfenbrenner (e.g. 1979) have pointed to the pivotal developmental role played by ongoing reciprocal social interactions (proximal processes) that occur fairly regularly and over extended periods of time. Joint attention and parent-child book reading are among the proximal processes/shared activities that have been argued to promote early vocabulary development (e.g. Baldwin, 1995; Ninio & Bruner, 1978).

Joint or shared attention involves the practice of sharing attention (usually visual) by following the focus of another person’s attention or by drawing their attention to one’s own focus of attention (Williams, Whiten, Suddendorf, & Perrett, 2001). Joint attention has developmental foundations in patterns of parent–child socio-emotional engagement in early infancy (Farrant, Maybery, & Fletcher, 2011; Racine & Carpendale, 2007). Parents play a pivotal role in this developmental process. Beginning in their earliest interactions parents do things to establish eye contact with their infants (Keller & Gauda, 1987; Keller & Zach, 1993) and infants respond with increases in looking and gazing at their caregivers between birth and around 3 to 4 months (Keller & Zach, 1993). Eye contact is an important component of socio-emotional engagement (Beier & Spelke, 2012) and parent–infant eye contact plays a role in the development of socio-emotional reciprocity during face-to-face interactions which emerges around 6 to 8 weeks of age (Adamson, 1995). Parent–infant eye contact and socio-emotional reciprocity facilitate the mutual regulation of emotions and interests. These mutual regulation skills allow objects to be increasingly incorporated into parent–infant routines and games between 3 and 6 months of age (Trevarthen & Hubley, 1978) and infants respond to this by developing the ability to follow other people’s head turns to a target in the infant’s visual field (Leekam & Moore, 2001).

These skills are further developed such that infants can follow other people’s points or head turns to a target that is out of their visual field by around 9 months of age (Butterworth, 1991; Butterworth & Cochran, 1980; Corkum & Moore, 1998; Scaife & Bruner, 1975) and they can follow an adult’s focus of visual attention to an object (using cues such as the adult’s gaze direction) to find the target of the adult’s emotional outburst and make mappings between objects and affective states by 12 months of age (Moses, Baldwin, Rosicky, & Tidball, 2001). This skill is further elaborated by 16 months of age such that children are able to learn word–object mappings when an adult follows the child’s focus of visual attention to the object before uttering the word (Baldwin, 1991, 1993b) and can follow the adult’s focus of visual attention to an object and learn word–object mappings by around 18 to 20 months of age (Baldwin, 1993a, 1993b; Baldwin, Markman, Bill, Desjardins, & Irwin, 1996). The provision of a language model (spoken words and phrases) during episodes of joint attention provides an effective way for children to learn word–object mappings (Tomasello & Todd, 1983). The findings of a number of studies support the importance of verbal labelling (Stevens, Blake, Vitale, & Macdonald, 1998) and joint attention for early vocabulary development (Dunham, Dunham, & Curwin, 1993; Farrant & Zubrick, 2011; Saxon, 1997; Tomasello & Todd, 1983) with some evidence indicating that at-risk children (e.g. those born prematurely) may be less responsive to the social world and therefore harder to engage (Salerni, Suttora, & D’Odorico, 2007).

Parent–child picture book reading simultaneously involves pointing gestures, joint attention and verbal labelling (Luo, Snow, & Chang, 2011; Murase, Dale, Ogura, Yamashita, & Mahieu, 2005) and provides an opportunity to learn word–object mappings in a more structured, reciprocal setting. As children’s vocabulary expands, parent–child book reading offers opportunities for children to learn the meanings of new words in terms of their existing vocabulary. Indeed, research has found that children use a richer vocabulary during episodes of parent–child book reading (Hoff, 2010). The findings of two meta-analyses support the efficacy of parent–child book reading as a means of promoting children’s vocabulary development (Bus, van Ijzendoorn, & Pellegrini, 1995; Mol, Bus, de Jong, & Smeets, 2008) with some research indicating that vulnerable children may require greater exposure to parent–child book reading in order to reap the benefits (Laakso, Poikkeus, Eklund, & Lyytinen, 2004). More recent research has found that joint attention and parent–child book reading predict children’s vocabulary development at 3 years of age and that these proximal processes mediate the effects of individual (e.g. maternal education) and environmental (e.g. number of siblings) characteristics (Farrant & Zubrick, 2011).

Thus, there is empirical evidence that joint attention and parent–child book reading facilitate early vocabulary development. What remains to be investigated is the extent to which low levels of joint attention in infancy and parent–child book reading across early childhood increase the risk of children having poorer vocabulary around the time of school entry. Answering this question would provide important information for the evolution of evidence-based policy and practice aimed at improving school readiness, particularly for children from disadvantaged backgrounds.

The aim of the current study was to address this. It was predicted that low levels of joint attention in infancy and parent–child book reading across childhood would be associated with a significantly increased risk of poor vocabulary in the early school years. Growing Up in Australia: the Longitudinal Study of Australian Children (LSAC) provides a valuable opportunity to address the current research question. LSAC includes data pertaining to joint attention around 9 months of age, parent–child book reading at approximately 21, 34 and 58 months of age, and child receptive vocabulary at around 58 months of age.

Method

Participants

The original LSAC sample was broadly representative of all Australian children (Harrison, McLeod, Berthelsen, & Walker, 2009). Details regarding the rationale, sampling, recruitment and data collection for LSAC have been reported by Gray and Sanson (2005) and Harrison et al. (2009). The analyses for the current article are based on waves 1, 1.5, 2 and 3 data from the infant cohort of children who had a median age of 9 months (M age = 8.8 months, SD = 2.6 months) at the commencement of the LSAC project, a median age of 34 months (M = 33.9 months, SD = 2.9 months) at wave 2 and a median age of 58 months (M = 57.6 months, SD = 2.9 months) at wave 3. At wave 1 in 2004 the infant cohort was comprised of 5107 children (2610 boys). These children were involved in subsequent waves where possible. In 98.7% of the cases the parent who completed the wave 1 interview was female and 99.7% were a biological parent of the study child. Hence the vast majority of parents interviewed were the biological mothers of the study children.

Measures

Child vocabulary

Child receptive vocabulary was measured at wave 3 using a short version of the Peabody Picture Vocabulary Test-III (PPVT-III, Dunn & Dunn, 1997) adapted for use in the LSAC study (Rothman, 2003). For the PPVT-III, children are asked to choose the picture that most closely matches the word said by the interviewer. Scores on the short version of the PPVT-III were transformed to a scale with a mean of 64 and a standard deviation of 8 (Rothman, 2003). To account for the effect of age of assessment at wave 3, poor vocabulary development was defined as being in the bottom 20% of vocabulary scores within the relevant age group category. Following Sanson et al. (2005), the five age group categories used were: less than 55 months, 55–56 months, 57–58 months, 59–60 months and more than 60 months.

Joint attention

Joint attention was assessed at wave 1 using a scale comprised of four items from the Communication and Symbolic Behaviour Scales (Wetherby & Prizant, 2002). The questions were: (1) When you look at and point to a toy across the room, does this child look at it? (2) Does this child try to get you to notice interesting objects – just to get you to look at the objects, not to get you to do anything with them? (3) Does this child show objects to you without giving you the object? (4) Does this child point to objects? Mothers rated the frequency of the described behaviour on a three-point scale ranging from (1) not yet to (3) often. For the present sample, the reliability of the joint attention scale was acceptable (α = .75). Scores on the four items were summed to give an overall score. For the current study, overall scores of 4 to 6 were classified as low, scores of 7 to 9 as mid-level, and scores of 10 to 12 were classified as high. We selected these cut-offs so as to produce three categories covering equal ranges of scores.

Parent–child book reading

The duration of parent–child book reading was measured via a mail-out questionnaire between waves 1 and 2 (wave 1.5) and during the parent interviews at waves 2 and 3. At wave 1.5 parents answered a single item (‘On average, about how many minutes per day is your child read to at home?’) on a five-point scale ranging from fewer than 5 minutes/day, 6–10 minutes/day, 11–20 minutes/day, 21–40 minutes/day, to more than 40 minutes/day. At waves 2 and 3 parents responded to two questions. The questions were ‘In the past week, on how many days have you, or an adult in your family, read to the child from a book?’ and ‘For about how many minutes is the child usually read to at a sitting?’ Mothers rated the first item on a four-point scale ranging from not in the past week (0) to 6–7 days (3) and the second on an eight-point scale ranging from child doesn’t like to be read to at all (0) to more than 60 minutes (7). For the present study responses to the two questions at waves 2 and 3 were combined to produce a new variable representing the average number of minutes per day of parent–child book reading at each wave. For the present study responses at each of the three waves were dichotomised such that 10 or fewer minutes/day was considered indicative of a low amount of parent–child book reading. This enabled a summary variable to be produced which represented the pattern of low and high amounts of parent–child book reading across the three waves.

Covariates

A number of family, maternal and child variables that may influence language development were included as covariates (Table 1). The number of children’s books in the home was measured at waves 2 and 3 using a single item (‘About how many children’s books does the child have in your home now, including any library books?’) which mothers rated on a five-point scale. Low levels of child approach-sociability and cooperation temperament (Sanson, Prior, Garino, Oberklaid, & Sewell, 1987; Smart & Sanson, 2005), warm parenting, family income, and community socioeconomic status (ABS, 2004) were defined as scores that were one standard deviation or more below the mean. A high level of child irritability temperament (Sanson et al., 1987; Smart & Sanson, 2005) was defined as a score that was one standard deviation or more above the mean.

Table 1.

Predicted risk for poor wave 3 vocabulary.

	M (SD)or %	% children with poor vocabulary	Adjusted odds ratio	95% confidence interval
Joint attention (wave 1)
Low	40.8%	15.7%	1.68^*	1.12–2.51
Mid	38.2%	15.8%	1.70^*	1.17–2.47
High	21.0%	10.6%	Ref
Parent–child book reading
Low wave 1.5, low wave 2, low wave 3	25.6%	23.1%	2.51^†	1.70–3.71
Low wave 1.5, low wave 2, high wave 3	7.4%	19.3%	2.32^*	1.39–3.86
Low wave 1.5, high wave 2, low wave 3	5.7%	11.9%	1.46	0.78–2.74
Low wave 1.5, high wave 2, high wave 3	7.9%	9.1%	0.99	0.54–1.81
High wave 1.5, low wave 2, low wave 3	10.8%	16.9%	1.68^*	1.04–2.72
High wave 1.5, low wave 2, high wave 3	8.0%	12.6%	1.53	0.89–2.63
High wave 1.5, high wave 2, low wave 3	9.1%	12.1%	1.51	0.89–2.56
High wave 1.5, high wave 2, high wave 3	25.6%	7.9%	Ref
Number of children’s books in the home
≤ 20 wave 2, ≤ 20 wave 3	3.0%	44.4%	3.24^†	1.88–5.57
≤ 20 wave 2, 21+ wave 3	7.1%	33.1%	2.63^†	1.81–3.82
21+ wave 2, ≤ 20 wave 3	1.7%	35.0%	2.46^†	1.20–5.03
21+ wave 2, 21+ wave 3	88.1%	11.8%	Ref
Low birth weight (< 2500g)	4.2%	22.2%	1.21	0.62–2.34
Premature birth (≤ 36 weeks)	5.7%	19.9%	1.02	0.56–1.87
Intensive care after birth	15.7%	19.3%	1.38	0.97–1.95
Male child gender	51.1%	16.8%	1.55^†	1.20–1.98
Firstborn child	42.7%	13.4%	0.91	0.69–1.19
Hearing problems (wave 1)	0.3%	57.1%	10.12^*	1.98–51.73
Low approach-sociability temperament (wave 1)	15.2%	18.1%	1.15	0.82–1.61
Low cooperation temperament (wave 1)	20.5%	12.2%	0.69^*	0.50–0.97
High irritability temperament (wave 1)	13.2%	13.4%	0.80	0.54–1.19
Main language spoken at home (LOTE, wave 1)	6.8%	37.7%	3.10^†	2.10–4.57
Maternal education (wave 1)
Year 10 or less	6.7%	25.2%	1.35	0.87–2.09
Year 11 or 12	17.9%	16.3%	1.17	0.85–1.60
Post secondary school	75.4%	13.4%	Ref
Maternal age at birth (years)
Teenage	1.1%	46.2%	5.04^†	2.11–12.05
35+	74.4%	13.1%	0.84	0.63–1.14
20–34	24.5%	14.7%	Ref
Low warmth parenting (wave 1)	14.9%	17.0%	1.08	0.77–1.50
Single parent (wave 1)	5.2%	27.4%	2.00^*	1.26–3.16
Low family income (wave 1)	7.8%	17.3%	1.15	0.75–1.78
Low community socioeconomic status (wave 1)	15.2%	16.4%	0.95	0.68–1.33
Child age at wave 3 (months)	58.02 (2.45)	–	1.05	0.99–1.11

p < .05, ^†p < .001, N = 2369, Ref = reference category, low parent–child book reading = 10 or less minutes/day. LOTE = languages other than English.

Results

Complete sets of the relevant data were available for 2369 children (1211 boys) who had a median age of 9 months (M age = 9.3 months, SD = 2.5 months) at wave 1. Consistent with previous research (e.g. Farrant & Zubrick, 2011), the group of children for whom complete data were not available (not included children) were from more disadvantaged backgrounds than the children for whom complete data were available (included children). The not included children had mothers that were significantly younger and less educated, had lower household incomes and community socioeconomic status, were more likely to be a single parent, had fewer children’s books in the home and were more likely to have a language other than English as the main language spoken in the home and to have low levels of parent–child book reading. The not included children were significantly more likely to have been born prematurely, have low birth weight, been in intensive or special care after birth and have high irritability temperament. The included children were significantly more likely to have low cooperation temperament and were less likely to have poor wave 3 vocabulary.

Because our aim was to quantify the increased risk of poor vocabulary associated with low levels of joint attention in infancy and parent–child book reading across childhood after controlling for relevant covariates, multinomial logistic regression was chosen as the appropriate analytic technique. A benefit of this technique was that categorising the data enabled a summary variable to be produced which represented the pattern of low and high parent–child book reading across the three time points. Doing this avoided the multicollinearity issues that would have arisen if we conducted a multiple regression analysis involving three continuous measures of parent–child book reading.

The hypothesis that low levels of joint attention in infancy and parent–child book reading across childhood would be associated with a significantly increased risk of poor vocabulary in the early school years was tested using the data for the included children. The results of a multinomial logistic regression that included the covariates indicated that, as hypothesised, children with a low joint attention score at wave 1 were significantly more likely to have poor vocabulary at wave 3 (see Table 1). Indeed, relative to those children in the high joint attention group, both low- and mid-level joint attention scores significantly increased the risk by around 70%. Around 16% of the children with low- and mid-level joint attention scores at wave 1 had poor vocabulary at wave 3, compared to 10.6% of the children in the high joint attention group (see Table 1). Consistent with the hypothesis, the multinomial logistic regression analysis also revealed that children who had low levels of parent–child book reading across waves 1.5, 2 and 3 were two and a half times more likely to have poor vocabulary at wave 3. As can be seen in Table 1, nearly a quarter of the children who had low levels of parent–child book reading across the three waves had poor vocabulary at wave 3 compared to fewer than 8% of the children who had high levels of parent–child book reading at each wave. Furthermore, children who had low levels of parent–child book reading at waves 1.5 and 2 or at waves 2 and 3 were also at a significantly increased risk (see Table 1). Having 20 or fewer children’s books in the home at wave 2 and/or 3 was also associated with a significantly increased risk of poor vocabulary at wave 3. The only protective factor was having low cooperation temperament. Other significant risk factors were male gender, hearing problems, having a language other than English as the main language spoken at home, having a teenage mother and coming from a single-parent family (see Table 1).

Discussion

The current study investigated the developmental importance of joint attention and parent–child book reading for children’s vocabulary around the time of school entry. As predicted, children who had low levels of joint attention in infancy were significantly more likely to have poor receptive vocabulary at wave 3. These findings are consistent with previous research that has supported the importance of joint attention for children’s vocabulary development (Dunham et al., 1993; Farrant & Zubrick, 2011; Saxon, 1997; Tomasello & Todd, 1983). Although correlation does not demonstrate causation, convergence between the findings of correlational analyses of real-world relationships and the results of training studies allow more powerful inferences to be made because the particular strengths of each type of research compensate for the weaknesses of the other (Bradley & Bryant, 1983; Harris, 2005). Thus, combining the present results with previous findings that joint attention training improves the communicative ability of children with autism (Isaksen & Holth, 2009; Jones, Carr, & Feeley, 2006; Rocha, Schreibman, & Stahmer, 2007; Whalen, Schreibman, & Ingersoll, 2006) and that joint attention training for childcare staff fostered typically developing children’s language development (Rudd, 2003) provides some convergent support for the role of joint attention.

In the current study children who had low levels of parent–child book reading across waves 1.5, 2 and 3 were two and a half times more likely to have poor vocabulary at wave 3. There was also some indication that children who had a low level of parent–child book reading at more than one wave were also at increased risk; children who had low levels of parent–child book reading at waves 1.5 and 2 or at waves 2 and 3 also had a significantly increased risk. The current results also underscore the importance of having more (e.g. > 20) rather than fewer children’s books in the home from an early age. Consistent with these findings there is evidence that interventions that provide children’s books and instruction which increase the frequency and quality of parent–child book reading have a positive effect on the vocabulary development of disadvantaged children (e.g. Taverne & Sheridan, 1995). Similarly, instructing parents or teachers in adult–child book reading facilitates the language development of children with language delays (Crain-Thoreson & Dale, 1999). Thus, there is convergent evidence indicating that parent–child book reading plays a causal role in children’s vocabulary development.

Consistent with previous research indicating that child temperament influences language development (e.g. Noel, Peterson, & Jesso, 2008) having low cooperation temperament was found to be a significant protective factor in the current study. The current finding of a relation between hearing problems and language delay has been well documented as has the relation between gender and language acquisition (e.g. Berglund, Eriksson, & Westerlund, 2005). Other significant risk factors identified in the current analyses were having a language other than English as the main language spoken at home, having a teenage mother and coming from a single-parent family. These results are consistent with previous research that has found that children’s vocabulary development is influenced by maternal age (e.g. Berryman & Windridge, 2000), home language environment (Rescorla & Achenbach, 2002) and family composition (Beitchman et al., 2008). Together these findings underscore the importance of the family environment for children’s early vocabulary development as well as the advantages of adopting a family-centred approach to intervention.

There are limitations in our findings. The group of children for whom complete data were not available (therefore not included in the analyses) were from more disadvantaged backgrounds than the children for whom complete data were available. The former had mothers that were significantly younger and less educated, more likely to be a single parent, had lower household incomes and community socioeconomic status, had fewer children’s books in the home, and were more likely to have a language other than English as the main language spoken in the home and to have low levels of parent–child book reading. The not included children were also more likely to have been born prematurely, have low birth weight, been in intensive or special care after birth and have high irritability temperament. The impact of this limitation may be in underestimating the effects of disadvantage on children’s vocabulary development. For example, previous research has found that less educated mothers point less during episodes of joint attention with their children (Rowe, 2000), that adolescent and low SES adult mothers differ from middle SES mothers in terms of the language they use when interacting with their children (Culp, Osofsky, & O’Brien, 1996; Lacroix, Pomerleau, & Malcuit, 2002), that low SES families have fewer children’s books in the home (Schiff & Lotem, 2011) and that children born prematurely have delayed vocabulary development (Kern & Gayraud, 2007). Future research should over-sample children from disadvantaged backgrounds to help avoid the limitations associated with non-random attrition in longitudinal research.

Another possible limitation of the current study is the use of maternal report measures of joint attention and parent–child book reading. Although social desirability cannot explain the pattern of results found in the present study it could be the case that it biases the reports in favour of higher levels of parent–child book reading and joint attention. It is difficult to know how parent reports of these differ from objective and independent measures. Furthermore, the measure of joint attention used in the present study is limited by the fact that it focused on the child’s behaviour rather than the interactions of the mother–child dyad. Future research using observational measures and/or a multi-method multi-informant approach would help confirm the current findings. Finally, it is important to recognise that while children with lower levels of joint attention and/or parent–child book reading sustain higher risks for low vocabulary on entry to school, the extent to which school ameliorates this cannot be observed in the data presented here. Studies able to longitudinally model vocabulary expansion, parent–child book reading and joint attention over time and particularly onward into the early school period would be very valuable indeed.

Practical implications

With these limitations in mind, the present findings further support the importance of joint attention and parent-child book reading for children’s vocabulary development. The evidence indicates that, beginning with eye contact in their earliest interactions, parents have ongoing opportunities to facilitate the development of joint attention and hence their child’s language development. Furthermore, because parent–child picture book reading simultaneously involves pointing gestures, joint attention and verbal labelling (Luo et al., 2011; Murase et al., 2005) it offers an excellent opportunity for developing joint attention skills and vocabulary expansion in a more structured setting (Farrant & Zubrick, 2011).

Building on the findings of meta-analyses that have underlined the importance of parent–child book reading for children’s vocabulary development (e.g. Bus et al., 1995; Mol et al., 2008) the current results indicate that it is important to initiate more than 10 minutes/day of parent–child book reading early in the child’s life and to continue this practice at least into the early school years. Other research has found that parents often miss opportunities to explain novel words when reading with their children (Evans, Reynolds, Shaw, & Pursoo, 2011) and that book reading training programmes can change adults’ book reading style to better facilitate children’s language development (e.g. Crain-Thoreson & Dale, 1999; Whitehurst et al., 1994). Thus, interventions that increase the amount and quality of parent–child book reading throughout early childhood can help prevent language development problems and thereby increase school readiness particularly among disadvantaged children. Indeed, the facilitative effects of family literacy programmes for disadvantaged children continue in the years following intervention (Phillips, Hayden, & Norris, 2006). Nevertheless, it is also important that personalised, structured treatment interventions of adequate intensity are available for children who arrive at preschool/kindergarten with delayed language development (Nelson, Welsh, Trup, & Greenberg, 2011).

Conclusions

The present study found that having low levels of joint attention in infancy increased the risk of poor receptive vocabulary in the early school years by around 70%; that having 20 or fewer children’s books in the home more than doubled the risk; and that children with low levels of parent–child book reading across early childhood were two and a half times more likely to have poor vocabulary development. These results converge with the findings of training studies which indicate that joint attention and parent–child book reading play causal roles in children’s language development. Thus, high priority should be given to educating current and future parents about the importance of parent–child book reading as well as the pivotal role they play in the development of joint attention.

Footnotes

Acknowledgements

The Longitudinal Study of Australian Children is funded by the Commonwealth Department of Families, Housing Community Services and Indigenous Affairs. We are grateful too for the support of the staff from both the Australian Institute for Family Studies and the Australian Bureau of Statistics. The authors wish to thank all of the children and families for their generous support and participation in the Longitudinal Study of Australian Children. This research was supported by a National Health and Medical Research Council of Australia Programme Grant (ID 572742). We also thank Kevin Durkin and the anonymous reviewers for helpful comments on earlier versions of this article.

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