Variable competence and performance in child second language acquisition1

The variable competence model of second language acquisition proposes that the ability to use language varies systematically within functional domains and linguistic contexts, and that such variability is inherent in interlanguage as well. This study of elicited and naturalistic speech of elementary school ESL students in formal and informal situations supports the conclusion that variability exists in the acquisition process but disputes the theory that it is a necessary com ponent of the mental competence itself. Errors in use of the past tense, noun phrase plurals and possessives, adjectives, and determiners were calculated for four different activities or tasks; t-tests and regression analyses revealed little or no statistical difference across tasks but predictable differences with increase in proficiency. Implications are drawn for the teaching of grammar to children in an academic context.