The present study focused on the differential effects of two German PD programs in the ECEC field. We examined whether PD programs are equally effective for all ECEC professionals or whether ECEC professionals benefit differently from these learning opportunities. An experimental pre-post-follow-up study was conducted in the field with random assignment of participants (N = 50) to one of two language-based PD programs. In addition, transfer-relevant factors (transfer motivation, self-efficacy, support from supervisors and colleagues) were taken into account to investigate whether possible differences in changes in the quality of instructional support were related to the transfer conditions. Using longitudinal multilevel analyses, we found that the PD program "Talking with Children", which focuses on language promotion strategies, is equally effective for all participants. Even with minimal perceived support from colleagues and supervisors, strategies learned in the PD program can be implemented to improve the quality of instructional support. Our results suggest the importance of considering transfer conditions to better support ECEC professionals in implementing what they have learned in PD programs in the future.