The mathematics achievement of seventh grade general education students placed in an inclusive setting with students in need of special education services was compared to the mathematics achievement of seventh grade general education students placed in a classroom without students in need of special education services. Participants included students from two suburban middle schools of the same school district in Southeastern Pennsylvania. Rasch Units from the Northwest Evaluation Association Measures of Academic Progress (NWEA, 2021) were used to compare growth between fall and winter administrations. Demographic identifiers of race and gender were included, and scores were examined in overall mathematics as well as the following subcategories: Algebraic Thinking, Real & Complex Numbers, Geometry, and Statistics and Probability. A causal-comparative ex post facto research design was used with data collected from the 2018-19 and 2019-20 school years. The data was analyzed using Analysis of Covariance in order to test significance of the two groups of students. The researcher found a significant difference (p < 0.05) in overall test scores between the two groups favoring the general education students placed in the co-taught setting. There was also a significant difference (p < 0.05) found in the subcategory of Algebraic Thinking, also in favor of the inclusion setting. In both instances, the effect size was small. No significant differences were found in the math scores of males, females, or any specific race of students. While this study adds to existing research on inclusion and co-teaching, further research is needed to determine if inclusion can be considered a best practice for all students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]