This article used self-regulated learning as a theoretical lens to examine the individual and interactive associations between a growth mindset and metacognition on math engagement for adolescent students from socioeconomically disadvantaged schools. Across three longitudinal studies with 207, 897, and 2,325 11-to 15-yearold adolescents, students' beliefs that intelligence is malleable and capable of growth over time only predicted higher math engagement among students possessing the metacognitive skills to reflect upon and be aware of their learning progress. The results suggest that metacognitive skills may be necessary for students to realize their growth mindset. Thus, growth mindsets and metacognitive skills should be promoted together to capitalize on the mutually reinforcing effects of each, especially among students in socioeconomically disadvantaged schools.Xu Qin and Juan Del Toro have equal intellectual contribution to this manuscript.This study was supported by funding from National Science Foundation #1561382 and #1315943 to the first author (Ming-Te Wang).Author contribution: Wang conceived of the study (e.g., study questions, study design, literature review, result interpretation, development of the writing outline), and drafted and revised the full manuscript; Zepeda conceived of the study and drafted and revised part of the introduction and discussion sections; Qin and Del Toro performed the data analysis, participated in the interpretation of the data, and drafted the method section; Binning participated in the result interpretation and provided feedback on the draft. All authors read and approved the final manuscript.