Children of mothers with elevated depressive symptoms may observe and learn a maladaptive cognitive style, including low perceptions of agency, that is, low perceived control over their emotions and circumstances. In turn, children may face increased cognitive vulnerability to depressive symptoms; however, this mediational model has yet to be tested. Using a longitudinal design and testing our hypotheses within a community sample, we investigated the mediating role of maternal agency in the associations between maternal depressive symptoms and child behavioral helplessness and depressive symptoms one and a half years later (M = 18.58 months, SD = 6.91 months). A diverse sample of school-age children (N = 137, 57.4% female, M_age = 9.74 years, SD_age = 1.51 years) and their mothers (N = 122) reported on their depressive symptoms at Time 1. A subsample of children and mothers returned to report on depressive symptoms at Time 2 (N = 68 dyads; 49 with complete data prior to multiple imputation). Maternal agency was coded from narrative responses to the Parent Development Interview–Revised for Parents of School-aged Children (Slade et al., 2009), completed at Time 1. Child behavioral helplessness was indicated by low strategy use at the end of a challenging puzzle task at Time 2. Results revealed that lower maternal agency predicted higher child depressive symptoms at Time 2 and mediated the associations between higher maternal depressive symptoms at Time 1 and higher child behavioral helplessness and depressive symptoms at Time 2. Implications for clinical intervention and future investigations are discussed. (PsycINFO Database Record (c) 2018 APA, all rights reserved)