IMPORTANCE Low-income minority children living in urban neighborhoods are at high risk for mental health problems and underachievement. ParentCorps, a family-centered, school-based intervention in prekindergarten, improves parenting and school readiness (ie, self-regulation and preacademic skills) in 2 randomized clinical trials. The longer-term effect on child mental health and academic performance is not known.OBJECTIVE To examine whether ParentCorps delivered as an enhancement to prekindergarten programs in high-poverty urban schools leads to fewer mental health problems and increased academic performance in the early elementary school years. DESIGN, SETTING, AND PARTICIPANTS This is a 3-year follow-up study of a cluster randomized clinical trial of ParentCorps in public schools with prekindergarten programs in New York City. Ten elementary schools serving a primarily low-income, black student population were randomized in 2005, and 4 consecutive cohorts of prekindergarten students were enrolled from September 12, 2005, through December 31, 2008. We report follow-up for the 3 cohorts enrolled after the initial year of implementation. Data analysis was performed from September 1, 2014, to December 31, 2015. INTERVENTIONS ParentCorps included professional development for prekindergarten and kindergarten teachers and a program for parents and prekindergarten students (13 two-hour group sessions delivered after school by teachers and mental health professionals). MAIN OUTCOMES AND MEASURES Annual teacher ratings of mental health problems and academic performance and standardized tests of academic achievement in kindergarten and second grade by testers masked to the intervention or control group randomization. RESULTS A total of 1050 children (4 years old; 518 boys [49.3%] and 532 girls [50.7%]) in 99 prekindergarten classrooms participated in the trial (88.1% of the prekindergarten population), with 792 students enrolled from 2006 to 2008. Most families in the follow-up study (421 [69.6%]) were low income; 680 (85.9%) identified as non-Latino black, 78 (9.8%) as Latino, and 34 (4.3%) as other. Relative to their peers in prekindergarten programs, children in ParentCorps-enhanced prekindergarten programs had lower levels of mental health problems (Cohen d=0.44; 95% CI, 0.08-0.81) and higher teacher-rated academic performance (Cohen d = 0.21; 95% CI, 0.02-0.39) in second grade.CONCLUSIONS AND RELEVANCE Intervention in prekindergarten led to better mental health and academic performance 3 years later. Family-centered early intervention has the potential to prevent problems and reduce disparities for low-income minority children. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT01670227