To investigate locus of control and its relationships to ethnicity, socioeconomic status (SES), and academic achievement, a large sample of Black, Mexican-American, Native American, and White students in the fourth, fifth, and seventh grades were administered the Academic Achievement Accountability Questionnaire (a locus-of-control questionnaire) and achievement tests. The locus-of-control instrument measured the degree to which the students felt responsible for their marks on tests and assignments and how important they believed studying was in determining achievement. As expected, greater internal locus of control was found for females and in the higher grades. Although internality was significantly related to both SES and ethnicity, SES exhibited the stronger effect on locus of control, significantly stronger for the White and Mexican-American subsample (the largest ethnically mixed subsample studied). Internality was associated with high achievement test scores, even with the other assessed variables controlled. (Author/MCG)