Content Summary : Since Carroll’s original work, interest in language universals and in natural language learning has tended to draw attention away fromindividual differences in aptitude. The issue has been raised again instudies by Skehan (1986b) in an attempt to deal with the underlyingcomplexity of language aptitude and its relation to first language acqui-sition and second language learning. Skehan’s work has been a follow-up to an earlier study of the first language development of two cohortsof children born in England in the Bristol area in 1969–70 and 1971–72(Wells 1985). The Wells study showed a great deal of variation inindividual first language development, so that, on the measures used,some children were years ahead of others. Skehan has been studying thesame children when they started to learn a foreign language at second-ary school, trying to find the relationships between their development offirst language proficiency, their foreign language aptitude (in particulargrammatical sensitivity and inductive language learning ability) measuredlater, and their actual achievement in learning a foreign language. Skehan’s studies have shown two strong predictors of the language aptitude that he measured when the children were aged 13. First was ‘ageneral language processing capability’: the children who had developedfaster in their first language (as shown by measures of sentence structurecomplexity and Mean Morpheme Length of Utterance) were those who