This study examined the longitudinal factor structure of general self-concept and locus of control among high school students over a 4-year period, with data from the National Educational Longitudinal Study of 1988. Measurement invariance was tested over time and across gender and ethnic groups; second-order piecewise latent growth models were applied to study changes. In all analyses, Likert-type scale items were correctly treated as ordered-categorical variables and methodology was used accordingly. Results suggested that the measurement structure of general self-concept and locus of control was stable over time and across groups. In addition, both constructs decreased and then increased during the 4-year period. The female group and the White group followed the pattern of changes of the total sample. The male group and the three ethnic minority groups (Asian/Pacific Islander, Hispanic, and Black) differed from the total sample in their change patterns. Further, group differences were observed in the two constructs at the base year.