Verbal operants in mothers' speech to nonretarded and Down's syndrome children matched for linguistic level.

Verbal response classes produced by mothers speaking to 21 nonretarded children were compared with those of mothers speaking to 21 Down's syndrome children matched with them on mean length of utterance. As mean length of utterance increased, total verbal response classes increased for both groups of mothers and children. Nonretarded children and their mothers produced more echoics; retarded children and their mothers produced more intraverbals. The implications of these findings were discussed in relation to previous research and the teaching of language.