This chapter investigates the perceptions, experiences and learning of native and non-native EFL teachers towards in-service teacher education (INSET) through critical friend group (CFG) in a language preparatory program, at a private high school in the western part of Turkey. Specifically, the study identifies the specific aspects of CFG which might enhance teacher-learning and finally, better understand their perceptions towards reflective practice. The participants were four EFL teachers offering English lessons in a preparatory class at the high school. Data were collected through interviews, video recordings, and reflective essays. The findings revealed that participating in CFG has promoted teacher-learning through collaboration as it became the vehicle that facilitated teachers to alter their classroom practices, which in return, supported the learning process in their classrooms.