Preparing students to become self-regulated learners has become an important goal of primary education. Therefore, it is important to investigate how we can improve self-monitoring and self-regulation accuracy in primary school students. Focusing on mathematics problems, we investigated whether and how (1) high- and low-performing students differed in their monitoring accuracy (i.e., extent to which students' monitoring judgments match their actual performance) and regulation accuracy (i.e., extent to which students' regulation judgments regarding the need for further instruction/practice match their actual need), (2) self-scoring improved students' monitoring and regulation accuracy, (3) high- and low-performing students differed in their monitoring and regulation accuracy after self-scoring, and (4) students' monitoring and regulation judgments are related. On two days, students of 9-10 years old from 34 classes solved multiplication and division problems and made monitoring and regulation judgments after each problem type. Next, they self-scored their answers and again made monitoring and regulation judgments. On the multiplication problems, high-performing students made more accurate monitoring and regulation judgments before and after self-scoring than low-performing students. On the division problems, high-performing students made more accurate monitoring judgments before self-scoring than low-performing students, but after self-scoring this difference was no longer present. Self-scoring improved students' monitoring and regulation accuracy, except for low- and high-performing students' regulation accuracy on division problems. Students' monitoring and regulation judgments were related. Our findings suggest that self-scoring may be a suitable tool to foster primary school students' monitoring accuracy and that this translates to some extent into more accurate regulation decisions.