Background and objectives <p>Delayed school start time (DSST) has been associated with prolonged sleep duration and reduced depressive symptoms. However, the overall magnitude of these effects remains unclear. We therefore conducted a systematic review and meta-analysis to assess the impact of DSST on sleep duration and depressive symptoms among middle and high school students.</p> Methods <p>We systematically searched Medline, Google Scholar, and Science Direct for studies examining the relationship between DSST and both sleep duration and depression. Four independent reviewers conducted risk-of-bias and quality assessments for each study. For quantitative synthesis, we calculated the standardized mean difference (SMD) using Hedges’s <i>g</i> to evaluate changes in sleep duration and depression.</p> Results <p>A total of six studies were included in the final meta-analysis. The pooled analysis indicated that DSST was associated with an average increase in sleep duration of 69&#xa0;min, with an SMD of 0.63, suggesting a moderate effect size. In contrast, analysis of depressive symptoms, based on five studies, produced a pooled SMD of − 0.20, indicating a smaller effect. Both analyses demonstrated high inter-study heterogeneity.</p> Conclusions <p>Our findings suggest that DSST is associated with a moderate improvement in sleep duration among middle and high school students, with minimal evidence of publication bias and small-studies effect, while depressive symptoms showed a small reduction. Further research with larger sample sizes and standardized outcome measures is warranted to clarify these associations.</p>