The purpose of this study was to examine the impact of Core Knowledge curriculum, a Comprehensive School Reform model, on the reading achievement of elementary students located in a north Texas suburban school district. A repeated measures, matched-comparison design was employed using longitudinal data over a three year period. Repeated measures analyses of variance (ANOVA) were conducted to determine if there were any significant differences in student achievement scores as measured by the Texas Assessment of Knowledge and Skills (TAKS) test. The experimental and control school were examined for student achievement gains overall, for advantaged versus disadvantaged students and for achievement gap differences. Although the results of the statistical analyses indicated that there were no significant differences in the reading TAKS scores of students participating in the study, experimental school students consistently had higher mean scores when compared to the control school in all areas. The evaluation of the achievement gap revealed that although the Core Knowledge school did not close the achievement gap between advantaged and disadvantaged students, the disadvantaged students' scores rose in proportion to the advantaged students, thus preventing an increase in the achievement gap between students.