Findings delineate differences between middle and high school students in the prevalence of adolescent sexual assault committed by peers. Approximately 50 percent of high school girls reported assault. Of those reporting assault, half reported less invasive forms of violence; the other half reported invasive assault, including rape, attempted rape, and forced oral sex. One-third of responding middle school girls reported less invasive assault; 10 percent reported more invasive sexual violence. One fourth of all boys reported assault, with all but 2 percent being less invasive forms of violence. Half of the girls reported being somewhat or very upset by the experience, in contrast to 13 percent of the boys. Half of all peer-on-peer sexual assault was perpetrated by a friend, but only 15 percent of acquaintance assault was perpetrated by a boy/girlfriend. The majority of acquaintance sexual assault occurred on school grounds, although assault on school grounds was less severe and was reported as less upsetting than assault occurring outside of school. Data were collected with a modified version of the Sexual Experiences Survey through a cross-sectional Web-based self-administered survey. All 7th through 12th grade students from a school district in southeastern Michigan were recruited to participate, with a 68.1 percent response rate. Tables and references