This study investigated mathematics teachers' professional knowledge among elementary school teachers exposed to a professional training program that either supported self-regulated learning (SRL) or offered no SRL support (no-SRL). The SRL support was based on the IMPROVE metacognitive self-questioning method that directs students' attention to understanding when, why, and how to solve problems (Kramarski and Mevarech, "Am Educ Res J" 40:281-310, 2003). Sixty-four Israeli elementary teachers participated in a month-long professional development program to enhance mathematical and pedagogical knowledge. The course was part of a 3-year professional development program sponsored by the Israeli Ministry of Education. This mixed-method study included quantitative assessments of teachers' professional knowledge in mathematical problem solving for an authentic task based on Program for International Student Assessment's framework (Program for International Student Assessment, 2003) and in lesson planning, as well as qualitative interviews and videotaped observations of two teachers. Results indicated that teachers in the SRL program outperformed those in the no-SRL program on various problem solving skills (e.g., reflection and conceptual mathematical explanations) and lesson planning (e.g., task demands and teaching approach). Videotaped observations of actual teaching indicated that the SRL-trained teacher demonstrated more teaching practices that aimed to promote students' understanding and better supported students' regulation of their own learning, compared to the no-SRL-trained teacher. We discuss educational and practical implications.