This study examines the correlation of physics conceptual inventory pretest scores with post-instruction achievement measures (post-test scores, test averages, and course grades). The correlation for demographic groups in the minority in the physics classes studied (women, underrepresented racial/enthic students, first generation college students, and rural students) were compared with their majority peers. Three conceptual inventories were examined: the Force and Motion Conceptual Evaluation (FMCE) (N = 2450), the Force Concept Inventory (FCI) (N = 2373) and the CSEM (N1 = 1796, N2 = 2537). While many of the correlations were similar, for some of the demographic groups, the correlations were substantially different. There was little consistency in the differences measured. In most cases where the correlations differed, the correlation for the group in the minority was the smaller. As such, pretest scores may not predict course performance for some minority demographic groups as accurately as they predict outcomes for majority students. The pattern of correlation differences did not appear to be related to the size of the pretest score. If pretest scores are used for instructional decisions that have academic consequences, instructors should be aware of these potential inaccuracies and ensure the pretest used is equally valid for all students.