Although research on the effectiveness of differentiated and enriched instruction in improving the achievement of diverse students is still emerging, some studies suggest that students in academically diverse classrooms benefited academically from differentiated learning experiences. The primary research question explored in this study was "What is the impact of implementing the pre-differentiated mathematics curricula in algebra, geometry and measurement, and graphing and data analysis on the achievement of grade 3 students, after controlling for pretest achievement scores?" Specifically, the authors were interested in examining whether math achievement outcomes of treatment and control group students differed. This study compared researcher-designed, pre-differentiated and enriched mathematics curricula in algebra, geometry, and measurement, graphing, and data analysis to the districts' mathematics curricula. The study concluded that, in general, the post-Iowa Tests of Basic Skills (ITBS) scores of students in the treatment group were equal to those in the control group. However, high-achieving students did appear to derive some benefit from the differentiated curricula. This was especially true for high-achieving students in lower-achieving schools. Future research should explore the differentiated units using different post-assessments, including the researcher-developed curriculum-based measures for both the treatment and control groups. Utilizing out of grade level assessments would have provided a clearer picture of the effects of the intervention. Tables and figures are appended.