This chapter presents evidence from secondary analysis of data collected during an evaluation of Thinking Maths, a professional learning program for teachers of middle years mathematics (Years 6–9). The South Australian Department for Education designed the program to develop teachers’ pedagogical content knowledge in order to improve students’ mathematical achievement. An evaluation in 2018 demonstrated that Thinking Maths had an impact on student achievement. In this chapter, I consider the impact of specific pedagogical strategies on students’ mathematical problem-solving capacity. Accordingly, this chapter focusses on the attitudinal, metacognitive, and process strategies taught in the Thinking Maths professional learning sessions. I present evidence that participating teachers adopted these high-gain strategies and that their improved classroom practices had an impact on students’ self-efficacy for mathematics problem solving over and above business-as-usual classrooms.