Class-size is one of the perennial topics of educational research and considered by many—especially teachers—as a key to improved learning results and student well-being. The accumulated research on class-size, however, has come out with vague and often controversial results. The internationally best known empirical class-size reduction study, the Tennessee STAR project, has been seen to support the benefits of smaller classes during the early grades especially for weaker students, seen to last until adulthood (Boyd-Zaharias 1999; Chetty, Friedman, Hilger, Saez, Schanzenbach, & Yagan, 2011), even if also critical comments have been presented based on secondary analyses of the data (Ehrenberg, Brewer, Gamoran, & Willms 2001; Hattie, 2005; Konstantopoulos, 2004). And contrary to the STAR-project,  the concurrent Indiana Prime Time project found that the early positive impact of smaller classes at grade one did not last beyond grade three (Gilman & Kiger 2003).

Also the results of European studies have been controversial. While Öckert & Oosterbeek (2012) report of register-data based positive impact of smaller classes of Swedish lower secondary students (even if long-term advantages seem only to regard higher SES students through the impact of smaller classes on their non-cognitive development), Leuven, Oosterbeek, & Rönning (2008) report on contrary results based on Norwegian data of the same age group. In their respective studies, centring on the possible mechanisms behind the alleged positive impact of class-size reduction, Hargreaves (19979 found that teachers often don’t take advantage of the smaller class by changing their teaching methods accordingly, while and Blatchford, Basset, Goldstein, & Martin (2003) found that even in bigger classes, teachers often organise their teaching by dividing the class to smaller groups of students. In their secondary analysis of the Dutch PRIMA data of grades 2, 4, 6, and 8, Dobbelstein, Levin, & Oosterbeek (2002) came to the conclusion that there was no or even a negative effect of smaller classes on student achievement. Using the IQ data included in the study they came to the conclusion that much of earlier class-size research has overlooked the impact of peer learning effect in the form of the impact of the help and challenge students get from class-mates whose level of ability is close to their own (see also Slavin, 1989).

In his synthesis of 500 meta-analyses regarding a plethora of factors related to or aiming at enhancing student achievement, John Hattie (2005) came to the conclusion that the impact of class-size reduction was tangential compared to the impact of many others with an average effect size of just 0,13 (Cohen’s d).

Despite the extensive research on class-size and its controversial results, class-size reduction looms continuously large in the discussion regarding the challenges of education in many countries. In Finland, where the average class size has constantly stayed slightly under the OECD mean, the Ministry of Education has supported municipalities in reducing class-size with special funding since 2009. Related to this, a study was conducted regarding the actual class size in the Finnish comprehensive schools based on a nationally representative sample of schools for grades 1-6 and 7-9 (Kupiainen & Hienonen, forthcoming).

Based on large scales assessments of the learning to learn competence (Hautamäki & Kupiainen, in press) of Finnish third-, sixth- and ninth-graders, this class-size study was extended to regard the relation between class-size and students’ transversal cross-curricular skills and their school- and learning-related attitudes, including their views on their teachers and the class they study in. Also the impact of students’ and/or their class-mates’ receiving of remedial or special support for learning, home-background (SES), and gender will be regarded in relation to class-size.

Blatchford, P., Basset, P., Goldstein, H., & Martin, C. (2003). Are Class Size Differences Related to Pupils’ Educational Progress and Classroom Processes? Findings from the Institute of Educa-tion Class Size Study of Children Aged 5–7 Years. British Educational Research Journal 29 (5), 709–730. Boyd-Zaharias, J. 1999. Project STAR. The Story of the Tennessee Class-size Study. American Educa-tor 23 (2), 1–6. Chetty, R., Friedman, J.N., Hilger, N., Saez, E., Schanzenbach, D.W., & Yagan, D. (2011). How does your kindergarten classroom affect your earnings? Evidence from project STAR. Quarterly Journal of Economics, 126 (4), 1593–1660. Dobbelsteen, S., Levin, J., & Oosterbeek, H. (2002). The causal effect of class size on scholastic achievement: distinguishing teh pure class size effect from teh effect of changes in class composition. Oxford Bulletin of Economics and Statistics, 64 (17), 17-38. Ehrenberg, R.G., Brewer, D.J., Gamoran, A., & Willms, J.D. (2001). Class size and student achievement. Psychological science in the public interest 2 (1), 1–30. Gilman, D.A. & Kiger, S. (2003). Should we try to keep class sizes small? Educational leadership 60 (7), 80–86. Hattie, J. (2005). The paradox of reducing class size and improving learning outcomes. International Journal of Educational Research 43 (6), 387–425. Hautamäki, J. & Kupiainen, S. (in press) Learning to learn in Finland. Theory and policy, research and practice. In Ruth Deakin Crick, Cristina Stringher & Kai Ren (Eds.) Learning to Learn. International perspectives from theory and practice. Routledge. Konstantopoulos, S. (2007). Do small classes reduce the achievement gap between low and high achievers? Evidence from Project STAR. Discussion paper. IZA DP No. 2904. Kupiainen, S. & Hienonen, N. (forthcoming). Luokkakoko suomalaisessa peruskoulussa (work title). Opettajankoulutuslaitoksen tutkimuksia. Helsingin yliopisto. Helsinki. Leuven, E., Oosterbeek, H. & Rønning, M. 2008. Quasi-experimental Estimates of the Effect of Class Size on Achievement in Norway. The Scandinavian Journal of Economics 110(4), 663–393. Slavin, R. E. (1989). Class size and student achievement: small effects of small classes. Educational Psychologist 24(1), 99–110. Fredriksson, P., Öckert, B., & Oosterbeek, H. (2013). Long-term effects of class size. The Quarterly Journal of Economics, 128(1), 249-285.