While many studies of monitoring accuracy have been conducted with college students, less is known about middle school students' monitoring accuracy, especially in Asian countries. Prior research also found discrepancies in students' monitoring accuracy between Western and Asian cultures. To understand and support Chinese middle school students' monitoring accuracy in mathematics, we implemented a three-week long monitoring intervention with 7th grade students in Southwestern China. Students were divided into three conditions: a control condition, a confidence rating condition (CR), and a confidence rating combined with monitoring instructions condition (CR + MI). Findings indicated that Chinese middle school students were slightly underconfident, yet quite accurate when monitoring during task completion in mathematics. Specifically, although students in the CR and CR + MI conditions did not show significant increases in mathematics performance, students in the control condition significantly decreased their performance overtime. In terms of monitoring, students' confidence bias increased overtime in the CR + MI and control conditions while students in the CR condition did not show significant change. Students also demonstrated increased self-reported metacognitive awareness across the three conditions. We also asked students to provide justifications for their confidence judgments. Findings indicated that students tended to consider a single factor when judging their performance during a mathematics task. Regression models of students' justifications indicated potential suggestions for future interventions. Implications and future directions are discussed.