Bigger Classes Mean Lower Marks: New Evidence Of The Impact Of Class Size
01 Dec 2010
Class size matters for student performance, particularly the most able students. That is the central finding of research by Professor Oriana Bandiera, Dr Valentino Larcinese and Professor Imran Rasul, published in the December 2010 issue of the Economic Journal.
By analysing data on the impact of class size on the final exam marks of graduate students in a leading UK university, the study finds that the effect of class size on students'' performance is, on average, negative. Everything else equal, a given student receives lower marks in courses with larger classes.
But, the researchers conclude, reducing class size is not always an effective strategy and is certainly not effective for all students in the same way. Reducing the size of very large modules – those with more than 100 students – could be a cost-effective way to improve performance, but not necessarily for class sizes below that.
The policy debate
The organisation of university education is increasingly in the spotlight both in academic and policy circles, especially given the Browne report on how universities should be funded. Most OECD countries have adopted policies that have led to dramatic increases in university enrolment. The average annual increase in university enrolment in OECD countries during the period 1995-2005 has been above 4%.
In the UK, this growth has occurred at both the undergraduate and graduate level, and across a wide range of universities. But the UK is actually at the low end of enrolment growth within the OECD. For example, between 1998 and 2005, the United States experienced a 30% increase in student enrolment.
Such breathtaking increases in enrolment inevitably lead to university students facing larger class sizes. Yet the effect of increasing class size in tertiary education is not well understood. While research on class size effects in primary and secondary schools provides useful guidance, the range of class sizes in universities is typically larger than at other tiers of the education system, and different mechanisms driving class size effects might operate.
Although tertiary education may involve more self-learning than primary or secondary education, class size remains solidly at the top of the policy agenda and concerns both faculty and students. This is particularly evident in the UK where concerns about increasing student-to-staff ratios have recently been expressed in a government report and by the most important unions of university teachers.
Data and methodology
The researchers estimate the impact of class size on the final exam marks of graduate students in a leading UK university between 1999 and 2004. As they observe the same student being exposed to very different class sizes, they can estimate the effects of class size on students'' exam performance by comparing the same student''s performance to his or her own performance in courses with small and large class sizes.
The estimates are therefore purged from confounding effects that arise because students choose which modules to take. For example, if more able students were to choose smaller classes, a cross-student comparison would capture both the effect of class size and the effect of student ability. The ''within-student'' comparison only captures the former.
The effect of class size on students'' performance is, on average, negative. A given student receives lower marks in courses with larger classes, everything else equal.
To get a sense of the magnitude of this effect, the estimates imply that a one standard deviation increase in class size from the mean – that is going from the average class of 56 to a class size of 89 – would decrease the mark by 9% of the observed variation in marks within a given student.
But these estimates mask two important forms of heterogeneity: first, the impact of class size varies across the range of class sizes; and second, the effect of class size varies across students.
Class size matters for student performance and particularly for the most able students. But reducing class size is not always an effective strategy and is certainly not effective for all students in the same way.
Reducing the size of very large modules (above 100) could be a cost-effective way to improve students'' performance. For modules in the range 30-100, reducing class size could be a rather ineffective strategy, while for classes below 30 it could be a valid but not necessarily cost-effective strategy.
The researchers conclude that attention should be devoted to other inputs in such cases and more refined and cost-effective solutions than pure number counting should be identified.
''Heterogeneous Class Size Effects: New Evidence from a Panel of University Students'' by Oriana Bandiera, Valentino Larcinese and Imran Rasul is published in the December 2010 issue of the Economic Journal.
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