Concern about the academic and social well-being of public education in the United States has been at the forefront of education reform. Increased class sizes, amended curriculum standards, and accountability standards have guided the way toward ways to reduce class sizes to meet the demands put upon educators. This study investigated the relationship among the Arizona Instrument to Measure Standards (AIMS) reading and math scores, class size, and socioeconomic status (SES) of students in Grades 3 to 5 in 2 schools. The research questions sought to determine whether class size or SES had an effect on student academic achievement, as evidenced by AIMS test scores. The study used archived, deidentified data and followed a causal-comparative research design. The data were analyzed using a repeated-measures MANOVA to determine whether there was a relationship between class size and the AIMS reading and math test scores. The findings will contribute to educational and social change by providing educators with referral information that can assist them in improving the educational experiences and academic achievement of all students. The findings derived from this study provide valuable knowledge useful to education reform. The study did find evidence of an interaction between the time that students participated in CSR and their AIMS scores in reading and math. Though class size and SES did not impact the AIMS scores that were studied, it is important to examine other effects such as ELL status, gender, and cultural identity. Changing the teaching standards and testing material during the study of archived data spanning 3 years also could have affected the results. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]