This study examined the interactions of teachers with different professional development (PD) backgrounds in communities of practice (CoPs) formed for student assessment in a South Korean middle school. We analyzed the teachers’ collaborative and reflective processes regarding the development, implementation, and feedback processes for student assessment in two CoPs that each consisted of two middle school science teachers. Two different types of CoP were identified: a routine practice CoP and a challenge practice CoP. The routine practice CoP displayed weak interaction between teachers and poor PD, while the challenge practice CoP displayed stronger interaction between teachers and better PD. These two types of CoP were determined by the mutual respect between the teachers. The results of this study can contribute to the development of teacher PD based on its implications for forming teacher CoPs that induce the active participation of members and the formation of mutually respectful relationships among them.