The Polytechnic of Wales Corpus was collected in the late 1970s for the study of syntactic and semantic development of native English-speaking children aged between six and twelve. This paper demonstrates that interesting lexical information can be gleaned from this corpus for EFL instructors and curriculum designers, even though the size of the corpus (61,000 words) makes it too small for dictionary development. The Corpus was organised to permit researchers to observe changes across age groups, and differences between the sexes and between children of different socio-economic backgrounds. Five investigations illustrate:
• rate of vocabulary growth with age in this Corpus;
• the extent to which vocabulary is sex-specific;
• differences between sexes in the use of affirmatives and negatives, and in the use of male and female personal pronouns;
• the extent to which vocabulary size is related to socio-economic class;
• persistence of errors in applying regular verb endings to irregular verbs.
The Corpus does show active vocabulary size increasing with age, at a rate of only around 50 words per year (in the limited activities used to elicit speech from the children). Surprisingly, around half of the words used by each of the sexes are limited to that sex. Boys make more use of positive expressions, whereas girls make greater use of negatives. Both sexes use he far more than she. There is no clear evidence that social class differences influence vocabulary size. Errors caused by applying regular verb endings to irregular verbs seem to diminish in children between ages six and eight, and have disappeared by age ten.
Although it is clear that data sparsity influences these results, they are still useful (and thought-provoking) to curriculum developers and coursebook designers in EFL, as well as researchers in sociolinguistics of child language.