This study examined whether a warm and positive classroom emotional climate would buffer the detrimental effects of maternal depression on children’s cognitive and socioemotional adjustment at first grade. Based on 1364 dyads, four waves of data spanning 6 months to first grade were used to examine paths between mothers’ early cumulative depressive symptoms and five first-grade outcomes (internalizing and externalizing behavior problems, social competence, academic functioning, and relationship with teachers). Classroom emotional climate was observed at first grade. Multiple group modeling revealed that children who were placed in a classroom that was characterized by a warm and positive emotional climate were shown to be less severely, or not, affected by mothers’ depressive symptoms in terms of the development of externalizing problems, social skills, cognitive performance, and relational functioning. Guided by the bioecological perspective, the current study showed synergic effects of intra-familial and extra-familial elements on an array of children’s developmental outcomes over time.