For educators seeking to differentiate instruction, cognitive ability tests sampling multiple content domains, including verbal, quantitative, and nonverbal reasoning, provide superior information about student strengths and weaknesses compared with unidimensional reasoning measures. However, these ability tests have not been fully evaluated with respect to fairness and validity for English-language learners (ELL). In particular, reliability is an important aspect of validity that has not been sufficiently evaluated. In this study, multivariate generalizability methodologies were used to explore the differential reliability of the Cognitive Abilities Test across ELL and non-ELL students in two schools with large Hispanic populations. Results suggest that verbal and quantitative reasoning skills are measured less precisely for ELL students than for non-ELL students. However, the composite score of the three batteries showed strong reliability in both groups. We conclude that multidimensional tests provide reliable information about the academic strengths of ELL and non-ELL students, though further research is needed. (Contains 6 tables, 1 figure, and 8 notes.)