Elementary teachers likely have many opportunities to improve their science subject matter knowledge in the context of their everyday work. However, this has not been sufficiently explored in the literature. The purpose of this exploratory study is to investigate teachers' self-regulated learning of science subject matter knowledge as a result of teaching experience. All teachers in this study recognized and described moments where they determined their subject matter knowledge was inadequate, an important step of self-regulated learning. Findings also indicate that teachers' recognition of gaps in their knowledge may be influenced by teachers' perceptions of the complexity of their students' questions. In response to recognizing gaps in their knowledge, teachers drew on online resources. They were, however, generally not critical about the quality of these resources. We discuss these observations in relation to teachers' self-regulated learning of science subject matter through teaching experience.