Self-regulated learning (SRL) is crucial to students' learning. SRL is characterized by students taking initiative, showing perseverance and adaptively regulating their learning. Teachers play an essential role in promoting and fostering this process. However, several studies have shown that in primary education explicit instruction of SRL strategies barely takes place. Given the relevance of SRL for learning and preparing students for the knowledge society of the 21st century, it is of crucial importance that teachers in primary education learn how they can improve their students' SRL. In the present study, we implemented a professional development program (iSELF) in which primary teachers were trained and coached in promoting and fostering their students' SRL. The extent to which iSELF contributed to teachers' explicit instruction of SRL strategies was evaluated in a quasi-experimental pre-test-post-test design using video-based classroom observations. Thirty teachers from fourteen different primary schools participated in this study and were assigned to either a control (twelve teachers) or an experimental group (eighteen teachers). Results indicate that in both conditions explicit SRL strategy instruction is rare. However, explicit instruction of SRL strategies is significantly higher in the experimental group on the post-test compared to the control group showing that teachers do benefit from learning about explicit SRL instruction.