This study aims to understand the role of self-regulated learning (SRL) and its different processes in the relationship between working memory (WM) and problem-solving accuracy in math in primary school children. A sample of 269 primary school children (M age = 8.84, SD = 0.81, 58% boys) participated in this study. Tasks were used as intervention resources to assess children’s WM (i.e., reading and computation span tasks), SRL (i.e., a digital game), and performance (i.e., the performance in the game, as well as a traditional math problem). Through structural equation modeling, results revealed that WM predicted children’s SRL and their problem-solving accuracy in math, such that those with higher capability for temporary storage attained better accuracy. Accordingly, children’s SRL explained the relationship between WM capacity and problem-solving accuracy in math; such that the indirect effect of WM capacity through SRL was lower on problem-solving accuracy in math. Results indicated that the planning phase was a greater indicator of students’ SRL in problem-solving accuracy in math. These results highlight the importance of SRL competencies in explaining children’s performance in problem-solving in math.