The purpose of this quantitative correlational research was to study the relationship between class size and students' academic achievement. Citywide language arts and math test scores for third and fifth grade students in four New York City public schools were examined using a variety of variables including (a) gender, (b) ethnicity, (c) grade level, (d) teacher experience, (e) classroom type (i.e., special education, inclusion/collaborative Team Teaching (CTT), gifted, or general), and (f) dollar amount spent for each student each year to determine if these variables played a significant role in the study. Conducting a partial correlation analysis, Zero Order Correlation Coefficients, Regression Coefficients, and Regression Analysis to test the hypotheses and to answer the research questions revealed that class size has no relationship to students' academic achievement. Conducting a regression analysis of class type demonstrated a class of 23 had a relationship to students' test scores, as the test scores were higher than the test scores of students in other classes. Female students performed better than male students in language arts and mathematics. Male Black students scored lower than any other ethnic group in language arts and mathematics. Teacher experience had an impact on students' performance in language arts and mathematics in grades 3 and 5. The results of the study indicated a need for further research including a longitudinal study using other variables to generalize whether class size has a relationship to students' academic achievement. [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.]