Research and common sense suggest that smaller classes offer teachers the chance to devote more time to each student, thus improving student learning. To explore the efficacy of improved teacher-student ratios, an overview of research on class sizes is offered in this report. An analysis of findings from initiatives in various states provides three broad conclusions: first, class-size reduction in the early grades leads to higher student achievement, with significant effects of class-size reduction appearing when classes contain somewhere between 15 and 20 students, and continue to increase as class size approaches a one-to-one ratio; second, if class size is reduced from substantially more than 20 students per class to below 20 students, the related increase in student achievement moves the average student from the 50th percentile up to somewhere above the 60th percentile; and finally, students, teachers, and parents all report positive effects from the impact of class-size reductions on the quality of classroom activity. However, class-size reduction represents a considerable commitment of funds, and its implementation can have a sizable impact on the availability of qualified teachers. (RJM)