This study found that students in settings with a year-round calendar statistically outperformed students with traditional calendars in a school-within-a-school setting in mathematics. The study included reading and math achievement of fifth graders in three school-within-a-school year-round elementary schools. Overall, the study made 16 comparisons of year-round and traditional student achievement and growth. When mean scores were compared in reading and math achievement and growth, all four comparisons favored year-round education. Only one difference, fifth grade national percentile rank in math, was statistically significant. When student-level variables were controlled, four reading comparisons were not statistically significant. All four math comparisons, however, were statistically significant.