We investigated the effects of a self-regulatory intervention strategy designed to improve middle-school students' calibration accuracy, self-regulatory skills, and math achievement. Focusing on self-monitoring and self-reflection as the two key processes of this intervention in relation to improving students' math achievement and overall self-regulation, we randomly assigned 30 sixth-and seventh-grade students to either a treatment or a delayed-treatment control group. At the conclusion of the intervention, we conducted interviews to unearth students' sources of calibration judgments. Results showed that participants who received the intervention had significantly higher math performance and predictive/postdictive calibration accuracy than did the control group. We provided educational implications of our findings for psychologists and educators.