Fig. 3. Delayed school start times are associated with higher grades, reduced sleepiness, and improved attendance and punctuality.

(A and B) Box plots of student performance and daytime sleepiness. Generalized linear models indicated that student performance, as measured by second-semester grades, was significantly higher (*P = 0.0261), whereas daytime sleepiness was significantly lower (*P = 0.0370) in 2017 than 2016. First-period absence (C) and tardy (D) data were compared between years using a χ² test. Students from FHS but not from RHS had a significant reduction in absences and tardies (*P < 0.0001) in 2017 as compared to 2016. Numbers within boxes in (A) and (B) represent medians, and numbers in bars in (C) and (D) represent absolute value.