ABSTRACTThe written compositions of 11-year-olds in the National Child Development Study were analysed using the T-unit length (Hunt 1965) as a measure of syntactic maturity, and composition length as a measure of productivity. Only a weak association was found between mean T-unit length (MTUL) and composition length. There were no statistically significant regional differences in either composition length or MTUL. There were statistically significant sex and social class differences in composition length but not in MTUL. Composition length was associated with Reading Comprehension, General Ability test scores, and teachers' ratings of certain scholastic aptitudes. MTUL was associated only slightly or not at all with these measures. The results are discussed in relation to cognitive and linguistic development.