Educational researchers have conducted numerous studies regarding the effects of class size on student learning, yet the disparity of their findings make it difficult to draw overall conclusions. This paper first provides a description of some of the major class size studies in an effort to illustrate this point. Next, a research approach is suggested which might yield more definitive conclusions by carefully accounting for the additional contextual factors which surround class size. In addition to giving particular attention to context, this involves focusing on the mediating effects between class size and achievement and measuring achievement with classroom-level assessments.The role of class size in student achievement in American education is a very contentious issue. Because class size cannot be reduced without incurring significant costs, adoption of a class size reduction program requires very careful consideration based on objective evidence. Evidence does exist which supports the assertion that smaller classes lead to greater student performance. At the same time, however, there is also ample evidence to the contrary. Given these conditions, the class size debate has become politicized. Lartigue (1999) writes that research is often "cherry picked" to support one's argument, with the proposed evidence driven by the attempt to substantiate the argument rather than to objectively contribute to the knowledge base. It becomes quite difficult to navigate the research to arrive at clear conclusions.The fact is that class size is an incredibly complicated construct. It may influence and be influenced by a host of factors that determine its effects. Berlin and Cienkus (1989) describe that size cannot be considered in a vacuum. The data seem to indicate that size factors have some influence on educational outcomes. But this influence is mediated by other factors (such as SES) and there are many social/political/geographic factors which determine the boundaries of school districts, the size of schools, and, of course class size (p. 228).