High school graduation is "not yet a reliable indicator of college readiness", (Gaertner & McClarty, 2015, p2). As such, researchers are investigating the use of non-cognitive factors as predictors of College and Career Readiness (CCR). The College and Career Readiness Mathematical Practice Scale (CCRMS) was designed to measure students' self-efficacy in the eight Standards of Mathematical Practice (CCSSI, 2015). Over 100,000 G8 and G10 students participated in the study. Construct validity analyses provided evidence that the CCRMS is reliable and justify the use of its scores for its intended purpose. A multi-level model was performed to assess the relationship between students' self-efficacy and achievement. After partialling out the variance due to prior achievement, student background characteristics, and student college-and-career aspirations, students' self-efficacy has a significant relationship with achievement. An investigation of self-efficacy scores revealed gaps in student self-efficacy across sub-groups; these gaps mirror those typically found in studies of student achievement. The implications for using the CCRMS measure as a diagnostic and evaluation tool to assess noncognitive interventions designed to improve student mathematics learning and achievement is discussed.