This longitudinal study examined the influence of parenting behaviors, well-being, and risk factors of low-income adolescent mothers on the cognitive and language abilities of children from infancy to age 3. Participants consisted of 1,240 mother-child dyads enrolled in the Early Head Start Research and Evaluation Project. Data were collected using structured interviews with the mothers and from videotaped mother-child interactions during play activities when children were approximately 14 months old and again at 36 months of age. Positive parenting behaviors exhibited toward the 14-month-old children predicted gains in both cognitive and language abilities more so than did maternal well-being, risk factors within the family setting, and demographic risk factors. Gains in cognitive abilities from infancy to age 3 were predicted by supportive parenting, higher family resources, and lower family conflict when children were infants. Gains in language abilities were predicted by supportive parenting, support for language and learning in the home environment, and higher family resources when children were infants. Finally, path analyses showed that maternal age had an indirect effect on child cognitive and language abilities at age 3 through effects on parenting behaviors. Older mothers were more likely to be supportive during play at age 14 months, which in turn promoted enhanced developmental outcomes at age 3. Implications for intervention and future research are discussed. (author abstract)