Class size and student achievement have been debated for decades. The vast amount of research on this topic is either conflicting or inconclusive. There are large and small scale studies that support both sides of this dilemma (Achilles, Nye, Boyd-Zaharias, Fulton, & Cain, 1994; Glass & Smith, 1979; Slavin, 1989). Class size reduction is a prominent intervention used in public schools to improve student achievement. The Clinton administration approved $1.6 billion provided to states to reduce class sizes. Eventually this money was rolled into other efforts with the passage of the No Child Left Behind Act in 2001 (Jacobson, 2008). Because this federal funding is no longer available to schools, districts must make decisions regarding the effectiveness of reduced class sizes in order to determine if such conditions should be continued. As public school budgets continue to decrease, this question becomes relevant for all. Without adequate information, school districts are being forced to make decisions about class sizes because of decreasing available funds for teachers' salaries. This study makes available some of that information by reviewing student achievement data as related to class size in a rural school district. This data is vital for considering district structures, organization of classrooms, and appropriate budgetary cuts. It also adds current information to the voluminous research on class size and achievement, with specific attention given to achievement of differing ability groups and genders in different class sizes. Quantitative data was gathered from standardized assessments for students in both large and small classrooms from third through fifth grades. PSSA math and reading scaled scores were used in this study for the purposes of identifying students' ability levels and comparing students' achievement. The effectiveness of small class size was determined by analyzing the pattern of mean test scores that result from PSSA reading and mathematics scores. Mean test scores from third, fourth and fifth grades were analyzed using analysis of covariance (ANCOVA). The third grade PSSA scores in math and reading were used as the covariate. Using ANCOVA statistically adjusted for any pre-existing difference, such as ability, found in the grade three baseline data when comparing to scores from grades four and five. Factorial ANCOVA was used for investigation into the other research questions, which allowed for the study of any interaction between other variables, namely the students' ability levels and gender. Results indicated smaller classes did not significantly affect student achievement in reading and math as measured by PSSAs in fourth and fifth grades for both cohorts. Grade three for the 2007-2008 cohort, however, did indicate students in the small class scored significantly better than those in the large class. Class size and ability level in regard to achievement in reading and math followed a similar pattern. There was no interaction in either cohort except in grade three reading scores from the 2007-2008 cohort. Additionally, no interaction was found between class size and gender in regards to reading and math achievement for any grade in either cohort. [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.]