The purpose of this study was to determine the effect of peer-based instruction on rhythm reading achievement of instrumental and choral music students attending a large urbanfringe high school in a major metropolitan area. Participants (N = 131) included band (n = 71) and choir (n = 60) students whose backgrounds reflected extensive economic (78% free or reduced lunch) and ethnic diversity (44% Hispanic, 31% Caucasian, 6% African American, 11% Asian/Pacific islander, 8% Native American). Using a randomized, post-test only experimental design, students were randomly assigned to one of two treatment conditions: traditional teacher-led instruction or reciprocal peer-based instruction. After a two-week instruction period, results show that students receiving peer-based instruction demonstrated significantly higher levels of rhythm reading achievement than students receiving traditional teacher led instruction. Factorial ANOVA analyses revealed that music reading self-concept did not significantly moderate rhythm reading achievement. A significant interaction was found between ensemble type (band/choir) and method of instruction (on rhythm reading achievement) with peer-based instruction effects on rhythm reading achievement noticeably stronger for choir students.