The purpose of this study was to investigate whether overweight students achieved a lower relative degree of scholastic achievement compared to nonoverweight students. Subjects consisted of 6th and 7th grade students enrolled in a large public middle school in a suburb of Philadelphia, Pennsylvania. We compared grade point averages (GPAs), nationally standardized reading scores, school detentions, school suspensions, school attendance, tardiness to school, physical fitness test scores, and participation on school athletic teams among nonoverweight, at risk for overweight, and overweight students. Overweight students achieved lower grades (P<0.001) and lower physical fitness scores (P<0.0001) than their nonoverweight peers. Overweight students demonstrated a 0.4 letter grade lower GPA (on a 4.00 scale) and 11% lower national percentile reading scores than their nonoverweight peers. The overweight students also demonstrated significantly more detentions, worsened school attendance, more tardiness to school, and less participation on school athletic teams than their nonoverweight peers. Our study suggests that body mass is an important indicator of scholastic achievement, attendance, behavior, and physical fitness among middle school students, reiterating the need for healthy lifestyle intervention and prevention measures.