Public opinion reflects a ‘common sense’ view that smaller classes improve student academic performance. This review reveals that the ‘class size’ effect of increased academic performance, although significant for disadvantaged students and students in the very early years of schooling, does not necessarily transfer to other student groups. Moreover, the literature indicates there are other more cost-effective variables that enhance student learning outcomes such as those associated with teacher quality. Internationally, large-scale interventions concluded that systematic class size reductions were more resource intensive requiring more personnel, training and infrastructure. From the large quantitative studies of the 1980s to the more qualitatively focused research in the last decade, there is a now an understanding that class size reductions function to provide opportunities for more student-focused pedagogies and that these pedagogies may be the real reason for improved student academic performance. Consequently, the impact of class size reductions on student performance can only be meaningfully assessed in conjunction with other factors, such as pedagogy.