There is a strong positive relationship between age and the number of social interactions a child is likely to initiate during a typical classroom free-play period. The type of interaction which shows the largest increase is verbally initiated child-child interactions. Verbally initiated child-teacher interactions also increase with age, though not so markedly as child-child interactions. There appears to be no significant change in non-verbal initiations of interactions with age, either to the teacher or to peers. These results give support to the use of observational techniques for language assessment in that they give further information about the growth of productive language skills as reported in a population survey of language abilities in mentally handicapped school children.