This study examined in-service teachers who engaged in a year-long professional development (PD) course that focused on conducting participatory action research (PAR) related to mathematics and science instruction. We focused on how the teachers perceived the PAR process and its impact on their practice and performance throughout the course. A multiple-case study approach was used and the data included interviews with teachers, observations, and teacher performance tasks. Four meta-design principles were implemented and embedded in the course: learning from and with peers, making thinking visible, making content accessible, and promoting autonomy to enable teachers to become lifelong learners. The findings indicate that a majority of the teachers acknowledged the opportunity to conduct PAR, cooperated with peers, changed their teaching strategies, and believed that they would continue to conduct PAR in the future. The findings support implementing PAR to improve teachers' teaching practices, PD perceptions, and performance of tasks during the course.