Insufficient sleep and sleepiness are common in adolescence and can negatively impact school performance. The current study examined sleep duration and sleepiness in academic performance and cognitive processes in early adolescence. Middle school students (N = 288; M[subscript age] = 12.01; 54% female; 48% Black, 37% White, 10% Hispanic) wore activity watches for seven nights, reported on daytime sleepiness, and completed computerized tests of attention and episodic memory. Academic performance was assessed with parent and teacher reports, and math and English/language arts (ELA) grades. Results revealed unique associations between daytime sleepiness and academic outcomes, but not cognitive processes. Both shorter and longer sleep duration were related to fewer academic enablers and lower academic skills and math grades. Students with the highest levels of academic performance occurred near 8 h of sleep per night. These results support the importance of addressing daytime sleepiness and optimal sleep duration in early adolescents.