This study aimed to explore the utility of a math curriculum-based measurement (M-CBM) to identify Spanish-speaking students at risk of math failure in third grade. The M-CBM includes a set of number sense based single and composite screening for third graders. The study's sample included 236 Spanish third-graders from the Canary Islands tested in the fall, winter, and spring. Reliability and validity of all measures were explored, finding adequate indexes. Receiver operating characteristics (ROC) and Hierarchical linear modeling analyses were conducted for both single and composite measures. All the measures revealed an area under the ROC curve values at or above 0.84, the composite measures ranging from 0.86 to 0.94. When comparing the single and composite measures, the latter revealed a higher classification accuracy for identifying students at risk in third grade than quantity discrimination, missing number, and multi-digit computation measures, but not for single-digit computation and place value measures. Finally, significant differences were found between at-risk and non-risk students learning growth throughout the school year.