Academic success in childhood is crucial for later academic, occupational, and life success (Heckman, 2006; Kuncel, Hezlett, & Ones, 2004; Spengler, Brunner, Damian, Lüdtke, Martin, & Roberts, 2015). Recent research suggests sleep is important for academic success but lacks objective measures of sleep (Buckhalt, El-Sheikh, Keller, & Kelly, 2009; Curcio, Ferrara, & De Gennaro, 2006; Dewald, Meijer, Oort, Kerkhof, & Bögels, 2010; Philbrook, Hinnant, Elmore-Staton, Buckhalt, & El-Sheikh, 2017). The purpose of this study was to examine the relations between sleep and academic success among children through objective measures of sleep in order to expand on the literature. Our sample consisted of 381 twins (50.4% male; 56% Caucasian; 36.5% same sex dizygotic) participating in an 8-year assessment from a longitudinal twin study. Actigraphy was used to assess sleep while various measures were used to assess academic success. A series of mixed model regressions were used to test the main predictions, with family entered as a random effect. Sex, age, Hispanic, SES, and zygosity were controlled for. Significant negative relations were revealed between sleep latency and reading and sleep latency and school liking. Additionally, SES was the most consistent significant positive predictor of our measures of academic success. These results suggest sleep and effects of SES should be considered when developing ways to help children’s school performance.