IMPORTANCE Low-income and minority mothers experience a disproportionate incidence of depression and lack access to treatment services. Development of prevention strategies in accessible community-based venues is a potentially important public health strategy. OBJECTIVE To determine the efficacy of a depression prevention strategy embedded in Head Start. DESIGN, SETTING, AND PARTICIPANTS This randomized clinical trial was performed from February 15, 2011, through May 9, 2016, at 6 Head Start agencies serving families at or below the federal poverty level. Participants included mothers with depressed mood, anhedonia, or depression history but who were not in a current major depressive episode. Participants were followed up for 12 months with masked outcome assessments. Final follow-up was completed on May 9, 2016. INTERVENTIONS Participants were randomized to a problem-solving education (PSE) intervention (n = 111) or usual Head Start services (n = 119). MAIN OUTCOMES AND MEASURES Primary outcomes were problem-solving skills and depressive symptoms. To capture the chronicity and intensity of symptoms, the Quick Inventory of Depressive Symptoms was administered bimonthly, and rates of clinically significant symptom elevations were compared across groups. Secondarily, the presence of a major depressive episode was assessed using the Structured Clinical Interview for DSM-IV Axis I Disorders. RESULTS Among the 230 participants, 152 (66.1%) were Hispanic, with a mean (SD) age of 31.4 (7.3) years. An intention-to-treat analysis among 223 participants contributing follow-up data found no differences in problem-solving skills across groups. The mean (SD) number of depressive symptom elevations among the PSE participants was 0.84 (1.39) compared with 1.12 (1.47) among the usual service participants (adjusted incident rate ratio [aIRR], 0.60; 95% CI, 0.41-0.90). In analyses stratified according to baseline depressive symptoms, PSE exerted a preventive effect among those with lower-level baseline symptoms, with a mean (SD) of 0.39 (0.84) elevations among PSE participants compared with 0.88 (1.37) among usual service participants (aIRR, 0.39; 95% CI, 0.21-0.75). However, no difference was observed among those with higher-level baseline symptoms (mean [SD] elevations, 2.06 [1.92] for PSE and 2.00 [1.91] for usual service; aIRR, 1.10; 95% CI, 0.67-1.80). Analysis of symptom scores followed the same pattern, with an adjusted mean reduction of 1.33 (95% CI, 0.36-2.29) among participants with lower-level baseline symptoms. CONCLUSIONS AND RELEVANCE The PSE intervention is efficacious in preventing depressive symptom episodes and performs optimally among those with initial low-level symptoms. Additional effectiveness studies in Head Start are necessary to develop meaningful public health programs. (author abstract)