We examined the roles of social support from adolescents' mothers and living arrangements in 197 adolescent mother–infant pairs. Major observational measures were teaching interactions, Home Observation for Measurement of the Environment (HOME) scores, and infant attachment security. Adolescents living with neither mothers nor partners had better teaching interactions but lower HOME scores compared with those living with mothers. High mother support was associated with more secure infant attachment only for those adolescents living with partners. When mother support was low, adolescents living alone had more secure infants than adolescents living with partners. Although parenting scores were related to differences in demographics and personal resources (intelligence and social skills), these did not appear to be responsible for the major findings.