This study evaluated the enduring effectiveness of a skill-based training program to enhance maternal sensitivity between 6 and 9 months of age. 82 mothers and their toddlers were evaluated at 18 and 24 months, and 79 at 31/2 years on the bases of observations of free play, everyday interaction, problem solving, and peer interaction. Most of the significant behavioral changes noted in the second year pertain to attachment security, indices of maternal sensitivity across situations, and child cooperation. Some enduring effects on indices of sensitivity appear to be attachment-mediated. In the third year, results revealed direct enduring intervention effects on parental responsiveness and child cooperation. Attachment-mediated effects were evident for maternal assistance, child security, and positive peer contact. Attachment pattern also predicted differences in attractiveness of the focal child as an interactive partner.