Across many countries, schools and classrooms are becoming culturally diverse. In response to this global trend, culturally responsive teaching (CRT) has been highlighted. Within this context, we have a two-fold goal in this study; to explore 1) whether and how pre-service teachers' international study experiences can impact their self-efficacy in multicultural classrooms when becoming practicing teachers and 2) whether and how in-service teachers' engagements in professional learning communities (PLC) can improve their self-efficacy in multicultural classrooms. Drawing on 2,714 Finnish teachers from 139 schools in the Teaching and Learning International Survey (TALIS) 2018, we found a positive relationship between teachers' study abroad experiences during their pre-service teacher education and their self-efficacy in multicultural classrooms. However, this significant result is not maintained with the addition of important variables. In contradistinction with this vanishing effect of teachers' study abroad experiences, we found that teachers' engagements in PLCs play a significant role in their self-efficacy in multicultural classrooms. We discuss implications of the contrasting findings for research and practice.