Do Small Class Sizes Have Any Impact?

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Class Sizes


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Do small class sizes improve student achievement in primary and secondary schools?

Increasing class size is one of the key variables that policymakers can use to control spending on education. I’ve tried my best to summarise this 110-page research document for the busy classroom teacher and school leader.

A modest return…

This systematic review examines the impact of class size on academic achievement. The review summarises findings from 148 reports from 41 countries. Ten studies were included in the meta-analysis. A total of 127 studies, consisting of 148 papers, met the inclusion criteria. These 127 studies analysed 55 different populations from 41 different countries and included pupils from nursery up to further education age.

The consensus among many in education research is that smaller classes are effective in improving student achievement which has led to a policy of class size reductions in a number of US states, the UK, and the Netherlands. This policy is disputed by those who argue that the effects of class size reduction are only modest and that there are other more cost-effective strategies for improving educational standards.

The impact?

The effectiveness of small class sizes for improving student achievement has been one of the most debated issues in educational research. One strand of class size research points to small and insignificant effects, another points to positive and significant effects. In this review, the intervention has been class size reduction. Studies only considering average class size measured a student-teacher ratio at school level (or higher levels) were not included.

This research suggests evidence that there is an effect on reading achievement, although the effect is very small. We found a statistically significant positive effect of reducing the class size on reading. The effect on mathematics achievement was negative and not statistically significant.


Class size reduction is costly and the available evidence points to no or only very small effect sizes of small classes in comparison to larger classes. Taking the individual variation in effects into consideration, we cannot rule out the possibility that small classes may be counterproductive for some students. It is therefore crucial to know more about the relationship between class size and achievement and how it influences what teachers and students do in the classroom in order to determine where money is best allocated.

  1. Overall, the evidence suggests at best a small effect on reading achievement.
  2. There is a negative but statistically insignificant effect on mathematics.
  3. Class size reduction is costly.
  4. The available evidence points to no or only very small effect sizes of small classes in comparison to larger classes.
  5. We should not rule out the possibility that small classes may be counterproductive for some students.


It is therefore crucial to know more about the relationship between class size and achievement in order to determine where money is best allocated. The research is published by the Campbell Collaboration, Norway (2018). You can download the full paper here.

There is a wealth of academic papers available here – search field terms include “2010+ and U.K.”. With a bit of investigative work, you may be able to refine this by subject and/or demographics.

9 thoughts on “Do Small Class Sizes Have Any Impact?

  1. This blog is misleading. When it states it does help but doesn’t with certain individuals it gives the same weight to the very small minority. Obviously, there’s not a one size fits all and other provisions should be in place for the individuals. Why should a whole class operate at the weakest link?

    Why are they spending on this when it just takes a quick survey from teachers?

    Easy answers to me….

  2. An interesting question with some insightful comments sitting behind the study, for example, “there are other more cost-effective strategies for improving educational standards.” Is this that old industrial model raising it’s ugly head again?

    Perhaps class size is not directly about educational standards and therefore using them as a measure is inappropriate. The quality and size of carrots in a1 sq meter of garden makes no allowance for the quality of soil, the irrigation or care lavished on them. But you can measure the carrots!

    What if we had a class size of 1, effectively the Bloom 2 sigma challenge? I would suggest then that the key element of the impact of class size becomes more evident and that it is ‘relationships’. We know, as teachers, that relationships sit behind student achievement so perhaps instead of measuring standards to determine the impact of class size, we should instead be looking at the quality and effectiveness of teacher/student relationships as the class size changes. The problem we have then, of course, is that this is not as easy to ‘measure’ directly and often takes time to filter through to results.

  3. I’d be interested to know whether effect size just focuses on student outcomes? Is teacher workload and therefore impact on other classes, planning/assessment time, teacher wellbeing etc. also taken into account when dealing with more students and thus more work?

  4. It is interesting that a feature of the majority of independent schools and also Universities such as Oxbridge, is that they have small groups……..

    In practical subjects larger groups are unsafe and very stressful for the teacher to manage leading to high staff turnover. A high price to pay.

  5. Id certainly say from experience that larger classes mean less one to one attention for pupils, more marking for the teacher and therefore increased workload.
    Without deeper discussions of an optimum class size it’s hard to really ‘prove’ class size makes a difference but teachers at the chalk face would always say it does I suspect.
    Ultimately it’s the quality of the relationships in a class which is the most important factor for me and as one of the previous commentators said this is far more difficult to evaluate.

  6. From someone who has taught 30 students to 7 in a class, this article does not take into account teach stress and work level. I would argue my mood was better and I could spend more time giving feedback and adapting learning to the smaller class size. The sample size cannot have been huge for this?

    1. Here is the link to the full paper. 6 studies, the sample sizes varied; the smallest study investigated 104
      students and the largest study investigated 11,567 students. On stress, this is the problem with most of these studies. They acknowledge additional workload, but fail to consider that large classes do influence, mood, personality, effectiveness etc. There are some studies..

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