Objective: This study was aimed at determining the external validity of the psychometric properties of a two-factor Collegiate Learning Assessment Performance Task Diagnostic Instrument (CLAPTDI) for use in assessing learning skills among predominantly black college students. The construct validity of the two factors CLAPTDI had been established in a previous study exploratory and confirmatory factor analyses. Establishing the external validity involved conducting a multi-group test of the measurement instrument's factorial scores equivalence across panels of lower class and upper class students from a predominantly black college. Method: The study relied on a strict test of equivalence categorization by focusing on tests for invariance across the two groups with respect to factor loadings, intercepts, and error factor loadings by estimating the difference in chi-square goodness-of-fit statistic and comparative fit index (CFI). Sets of measurement and structural parameters were put to the test in a logically ordered and increasingly restrictive manner. Results: The analyses found that the CLAPTDI scale's factorial measurement structure was invariant across lower class and upper class PBC students. Conclusion: The collegiate learning assessment performance task diagnostic instrument with two latent factors and five observed variables is a valid measurement scale for assessing the level of analytic reasoning and problem solving learning among predominantly black college students. Contribution/ Originality: The study is one of very few studies which have investigated the external validity of the psychometric properties of a two-factor Collegiate Learning Assessment Performance Task Diagnostic Instrument (CLAPTDI) for use in assessing learning skills among predominantly black college students.