ABSTRACT: Parental knowledge/monitoring is negatively associated with adolescents' depressive symptoms, suggesting monitoring could be a target for prevention and treatment. However, no study has rigorously addressed the possibility that this association is spurious, leaving the clinical and etiological implications unclear. The goal of this study was to conduct a more rigorous test of whether knowledge/monitoring is causally related to depressive symptoms. 7940 youth (ages 10.5-15.6 years, 49% female) at 21 sites across the U.S. completed measures of parental knowledge/monitoring and their own depressive symptoms at four waves 11-22 weeks apart during the COVID-19 pandemic. First, monitoring and depression were examined in standard, between-family regression models. Second, within-family changes in monitoring and depression between assessments were examined in first differenced regressions. Because the latter models control for stable, between-family differences, they comprise a stronger test of a causal relation. In standard, between-family models, parental monitoring and youths' depressive symptoms were negatively associated (standardized [Formula: see text]= -0.22, 95% CI = [-0.25, -0.20], p < 0.001). In first-differenced, within-family models, the association shrunk by about 55% (standardized [Formula: see text]= -0.10, 95% CI = [-0.12, -0.08], p < 0.001). The magnitude of within-family association remained similar when adjusting for potential time-varying confounders and did not vary significantly by youth sex, age, or history of depressive disorder. Thus, in this community-based sample, much of the prima facie association between parental knowledge/monitoring and youths' depressive symptoms was driven by confounding variables rather than a causal process. Given the evidence to date, a clinical focus on increasing parental knowledge/monitoring should not be expected to produce meaningfully large improvements in youths' depression.