The goal of this study was to provide normative scores and examine the psychometric properties of the Math Computation subtest of the Wide Range Achievement Test--IV (WRAT-IV) for Mexican adolescents after the completion of junior high school. We group-administered this subtest to 1,318 first-year Mexican high school students. We then obtained its overall internal reliability and examined its underlying factor structure. Finally, we determined its concurrent and criterion validity by evaluating a subsample of 106 students that included adolescents with mathematical difficulty, mathematical talent, and typical performance. Results showed that the subtest has a good internal reliability and appropriate psychometric characteristics, suggesting its appropriateness for the detection of adolescents with particular difficulty or ability in mathematics. The exploratory factor analysis identified three factors: arithmetic, fractions and basic algebra, and rational numbers. There were also sex differences in the number of correct responses, but the effect size was small.