Class sizes in the United States had been a topic of discussion throughout history. There had been mixed results on whether class sizes influenced student achievement or not. In the qualitative single-embedded case study, nine teachers were interviewed and given an open-ended questionnaire to determine if class sizes influenced student achievement. Teachers were given an open-ended questionnaire and then interviewed about how they perceive class sizes and their influence on student achievement. Five class size policies were analyzed to determine the similarities and differences. The findings showed that class sizes had a negative influence on student achievement. The research questions how teachers perceived class sizes influenced student achievement and what classroom management strategies teachers use when handling smaller and larger classrooms. The results indicated that larger class sizes have a negative influence on student achievement as teachers have a harder time meeting all the needs of the students. Smaller class sizes are preferred by teachers. Recommendations for future research and future policies are to continue to listen to teachers when creating policies. Teachers are the people in the classrooms, and they are the ones that should have their voices continue to be heard. [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.]