CUNNINGHAM, CHARLES E.; REULER, ELLEN; BLACKWELL, JANE; and DECK, JENNIFER. Behavioral and Linguistic Developments in the Interactions of Normal and Retarded Children with Their Mothers. CHILD DEVELOPMENT, 1981, 52, 62-70. This study examined the verbal and behavioral interactions of 18 normal and 18 retarded children with their mothers in 15-min free play and 15-min structured task situations. Groups were equated on the basis of Peabody Picture Vocabulary Test Scores (MA), sex, and socioeconomic status. Retarded children initiated fewer social interactions, were less responsive to their mother's interactions, and engaged in more solitary play than normal children. Mothers of retarded children were more directive during the play and task settings, initiated fewer interactions, and were less likely to respond positively to their child's compliant task-oriented efforts. In the retarded group, mothers of children with higher MA scores were less responsive to their children's interactions than those of children with lower MA scores. Children with higher MA scores interacted more frequently, were more responsive to maternal interaction, and were more compliant than children with lower MA scores. The complexity of maternal speech to the normal and retarded groups as measured in mean length of utterances (MLU) and developmental sentence scores (DSS) did not differ significantly. In both the normal and retarded groups, the MLU's of mothers to children with higher MAs were longer than those to children with lower MAs. In the normal group, the MLUs of children with higher MA scores were significantly longer than those of children with lower MA scores. In the retarded group, however, the MLUs of children with higher and lower MAs did not differ. A series of correlations suggested that variations in the relative match between the speech complexity of mothers and their children were related to a number of behavioral indices of reciprocity in the mother's interactions with the child.