1 Department of Education, Concordia University, Montreal, PQ, Canada. nina.howe@education.concordia.ca

Associations between siblings' reciprocal (i.e., play) and complementary (i.e., teaching) interactions in 70 sibling dyads (1st-born siblings' mean age=81.6 months, range=59-119 months; 2nd-born siblings' mean age = 56.1 months, range = 5-79 months) were examined. Dyads participated in 2 sessions (play, teaching) and completed a sibling relationship quality measure. Findings revealed modest associations across play and teaching sessions; for example, greater learner involvement in the teaching task was associated with more collaboration and less negative affect during play. In addition, the 2nd-born's teaching style was related to perceptions of relationship quality. Results indicate that reciprocal and complementary types of interactions may provide important contexts for development of individual differences in dyadic and individual behaviors and may afford opportunities for siblings to influence one another's development.