This study tested whether grade retention at the transition into secondary school had a significant impact on adolescent psychosocial adjustment. A quasi-experimental design was used in which propensity score matching was implemented. Univariate ANCOVAs were subsequently run on a subsample of 181 students enrolled in one typical secondary school in the French-speaking region of Belgium (M = 12.91 years, 55.8% girls). These analyses revealed that retained students experienced decreases in self-esteem, perceived parental support for competence and involvement in the relationships with their parents, and intrinsic and extrinsic motivation variables. Retained students also failed to show the decrease in delinquent and aggressive behaviors and social withdrawal that was observed in matched promoted students. In sum, grade retention appears to be detrimental to early-adolescence psychosocial adjustment. To decrease rates of grade retention among adolescents, change is needed in parents', school staff's, and policymakers' preconceptions that the practice has overall positive outcomes.