This study examines whether a relationship exists between school size and student achievement utilizing the Pennsylvania System of School Assessment (PSSA) exams for students in grades 3-8 in both Reading and Math. More specifically, the study investigates the relationship of school size and achievement with historically underperforming subgroups, such as students who are economically disadvantaged, have a disability, or belong to a minority category. The study finds that students with disabilities had significantly higher achievement in smaller schools than larger schools. In fact, students with disabilities are as much as 30% more likely to score proficient on standardized exams in smaller schools than larger. This study also indicates that economically disadvantaged students are as much as 20% more likely to score proficient on standardized exams in smaller schools than larger. On the other hand, the study shows that students belonging to a minority category are more likely to score proficient on standardized exams in the largest schools compared to smaller schools. For example, Black students can be 20% more likely to score proficient in larger schools than smaller schools, and Hispanic students are 15% more likely. Although a correlation appears to exist between school size and student achievement, many confounding factors could exist that may affect the relationship and limit causal conclusions, such as school resources, class size, school climate, and teacher attitudes. [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.]