A strongly held conviction in education research is that smaller class sizes are better for students. Surely a teacher can be more effective in a classroom with 20 students than in one with 30 students. Smaller class sizes have many potential benefits, such as students receiving more individualized attention from teachers, greater order in the classroom, and greater opportunities for class discussions and/or small-group work.
Indeed, in most cases, smaller classes are better. If we compare two classrooms that look identical except for the number of students, students with smaller class sizes have modestly higher standardized test scores than those in larger classes, in most cases.
Are class size reductions equally effective for all students, or do some groups of students benefit more than others? Often, students in early primary grades benefit more from smaller class sizes than students in later primary grades. For other characteristics such as race/ethnicity, gender, or parental income, the benefits of smaller classes are pretty similar. Girls do not benefit any more or less from smaller class sizes than boys, for example.
Reducing class size is an expensive policy, however. Consider a reduction in class size of five students, from 30 to 25. A large school with 150 students would need to increase the number of teachers from five to six, an increase of 20%. Plus, there are other costs to consider such as additional classroom space, more administrative overheads, etc. In nearly every study of class size, the conclusion is that the costs of smaller classes are larger than the benefits. In other words, educators are probably better off considering other ways to improve student outcomes, such as improving the quality of teachers, than simply reducing class sizes.
At the same time, there is a lot that we do not know about the potential benefits of reducing class size. For instance, in most developing countries, we have little idea about the benefits of smaller class sizes. How can we assume that a reduction in class size would have the same benefit for students in sub-Saharan Africa as it does for students in places like California or Sweden?
Nearly all research on reducing class sizes is for students in primary school. Again, we just do not know much about the benefits of smaller classes for students in secondary school, particularly in the later grades (i.e. “high school” in US terminology—grades 9 to 12). You can imagine how much we know about the benefits of smaller class sizes in later grades in developing countries—essentially nothing!
Class size: Does it matter for student achievement?, by Christopher Jepsen
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