This study examined the optimal timing (infancy, toddler-preschool, or both) for facilitating responsive parenting and the intervention effects on maternal behaviors and child social and communication skills for children who vary in biological risk. The intervention during infancy, Playing and Learning Strategies (PALS I), showed strong changes in maternal affective-emotional and cognitively responsive behaviors and infants' development. However, it was hypothesized that a 2nd intervention dose in the toddler-preschool period was needed for optimal results. Families from the PALS I phase were rerandomized into either the PALS II, the toddler-preschool phase, or a Developmental Assessment Sessions condition, resulting in 4 groups. Facilitation of maternal warmth occurred best with the PALS I intervention, while cognitive responsive behaviors were best supported with the PALS II intervention. Behaviors that required responsiveness to the child's changing signals (contingent responsiveness, redirecting) required the intervention across both the early and later periods. (Contains 8 tables.)