Journal ArticlePredictive Validity of the Algebra Concept Inventory (ACI): The Importance of Algebraic Conceptual Understanding to College Math and STEM OutcomesWladis, C; Sencindiver, B; Hachey, A C; Myszkowski, N; Offenholley, K; Samuels, J; Geillan, AThe Algebra Concept Inventory (ACI) is the first large-scale instrument validated to measure the foundational algebraic conceptual understanding of college students. This study uses ACI scores to conduct the first quantitative analysis on the relationship between algebraic conceptual understanding and college outcomes, thus exploring the predictive validity of the ACI. Specifically, we investigate whether ACI scores predict: (1) math course grades; (2) subsequent completion of math courses required for STEM majors; (3) completion of STEM versus non-STEM degrees; and (4) the extent that differences in these outcomes by race/ethnicity or gender are explained by ACI scores. Results indicate that ACI scores significantly predict math course outcomes and STEM versus non-STEM degree completion, as well as significant proportions of differences in these outcomes by race/ethnicity and gender. This illustrates the importance of providing every student instruction that supports development of the kinds of foundational algebraic conceptual understanding measured by the ACI.AERA Open2026-01-2710673552AERA open1211-302332-8584https://doi.org/1760491higher education, colleges, assessment, equity, mathematics education, hierarchical linear modeling, regression analyses, research in undergraduate mathematics education, concept inventories, algebra, conceptual understanding, predictive validity, STEM majorsNational Science Foundation