The purpose for this correlational, explanatory study was to explain the influence of the length of the school day on the mean Partnership for Assessment of Readiness for College and Careers (PARCC) scores on the 2016 Grade 8 Mathematics and 2016 Algebra II tests for students in various socioeconomic strata. The Grade 8 Mathematics sample included 150 public schools and the Algebra II sample included 166 public comprehensive high schools. The analyses controlled for various student, staff, and school variables. The results suggest that longer school days benefit students from wealthier school districts more so than students living in poverty or middle class students.