As popular music education programs become more common, it is essential to determine what kinds of professional development experiences that are designed to help teachers include popular music into their music education classrooms are effective--keeping in mind that the inclusion of popular music in K-12 classrooms requires a change not only in instrumentation and repertoire but also pedagogical approaches. This study examined the effects of a popular music professional development initiative on more than 600 New York City urban music teachers' musicianship, their pedagogy, and their leadership skills throughout one school year. Results revealed increases in all three areas, most notably in teachers' musicianship. The study also showed an increase in teachers' positive perceptions about their music programs, specifically, their level of excitement about the state of their music program and that their music program was more effective at meeting their students' needs than it had been previously.