The purpose of this study was to investigate the effectiveness of a beginning jazz improvisation learning environment for middle school instrumentalists, including whether one of two instructional sequences of harmonic form improvisation tasks better supported four outcomes: achievement, self-assessment, self-efficacy, and motivation. Over 12 weeks, fifth- to eighth-grade instrumentalists (n = 43) studied jazz improvisation in a learning environment with four critical features: (a) forming cooperative jazz combos, (b) making jazz thinking visible, (c) encouraging specific feedback, and (d) implementing harmonic form sequencing. Quantitative data for all outcomes were collected pre-, mid-, and postinstruction. Primary findings showed: (a) a significant effect on all outcomes over time, not only for the 12-week duration of the instructional period but even in the first 6 weeks; (b) a significant interaction between assessed task (i.e., a modal- or blues-based improvisation) and achievement; (c) evidence of transfer of learning when, midinstruction, participants significantly improved at both tasks after only studying one; and (d) no significant effect according to instructional sequence of harmonic form (i.e., modal/blues vs. blues/modal).