Childcare teachers' warm and sensitive responses play a critical role in infant development. Korean in-service systems do not sufficiently support the interaction quality of childcare teachers. This study examined previous in-service programs shown to improve the interaction quality of teachers and calculated the effect sizes of 38 in-service programs reported in Korean and English-language research, and explored their moderating factors. In-service programs had moderate effects on interaction quality, and mixed workshop-coaching programs had the largest effect size. Programs shorter than 1 month, or with more than 20 sessions or 4-6 h per session effectively improved interaction quality.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).