This study examined the predictive validity of a teacher rating scale called the Self-Regulation Strategy Inventory–Teacher Rating Scale (SRSI-TRS) and its level of convergence with several student self-report measures of self-regulated learning (SRL). Eighty-seven high school students enrolled in one of four sections of a mathematics course in an urban high school and one mathematics teacher participated in the study. Correlation analyses revealed moderate correlations between the SRSI-TRS and self-report questionnaires targeting students’ motivation beliefs (i.e., mathematics interest) and regulatory behaviors in mathematics. Students’ self-efficacy perceptions correlated with all SRL and achievement measures, but not the SRSI-TRS. Hierarchical regression analyses showed that the SRSI-TRS emerged as the primary SRL predictor of achievement although student reports of their maladaptive SRL behaviors was a significant predictor in the final model.