Does class size matter?

Professor Barnaby Lenon, Dean of Education, looks at the impact of class sizes.

Class sizes in the UK are quite large – an average of 25 at primary schools compared to an OECD average of 21.

There are mixed opinions amongst researchers about the merits of smaller class sizes. PISA research suggested that small class sizes do not raise standards. They point out that some of the highest-achieving jurisdictions have large class sizes, such as China with average primary class sizes of 37. Andreas Schleicher has often said that the policy should be to ‘put the best teachers in front of large classes’.

The Education Endowment Foundation Toolkit summarises the research in the UK and concludes that smaller class sizes raise standards, especially at primary level, but not by much and at tremendous cost.

But the American STAR Project (Student-Teacher Achievement Ratio), (Finn and Achilles, 1990) looked at a cohort of 12,000 students in Tennessee between 1985 and 1989. They found that small classes did better academically and especially benefitted minority ethnic pupils, so reducing the achievement gap.  The pupils were more engaged, they received more individual attention, there were fewer disciplinary problems. Smaller classes generated a stronger sense of group membership, children were more able to support each other, teacher stress and teacher turnover was less. Teachers spent less time on behaviour management and less time on paperwork.

The California Class Size Reduction (CSR) Program to reduce class size began in 1996 when California’s state legislature passed a reform aimed at cutting class size in the early school grades from what had been an average of 28 pupils to a maximum of 20. While the Tennessee STAR programme only involved 12,000 pupils, the California programme was implemented state-wide for 1.8 million students. Jepson and Rivkin (2002) found that, all else being equal, smaller classes raised student achievement. Reducing class size by 10 students raised the percentage of third-grade students who exceed national median test scores by about four percentage points in mathematics and three percentage points in reading.

However, all else is not equal when you hire thousands of new teachers. Pupils taught by the new teachers did LESS well than they would have done in larger classes with more experienced teachers.  Having a new teacher reduced the percentage of students who exceed the national median by roughly three percentage points in both mathematics and reading. So in many schools, class size reduction meant zero gain, at least in the short run. The bottom line was that California implemented a $1.6-billion-ayear programme that yielded only modest gains.

There is another important point about class size which is well analysed by Stevenson and Stigler (1992). Countries have finite resources to spend on education so there is always a trade-off between class size and hours spent teaching. In countries with smaller classes (America, the UK) simple economics means that teachers have to spend more time in front of pupils and have less time for preparation and CPD. In countries with larger classes like China (38–50 in a class) the system can afford to allow teachers to teach less and have more time to prepare.

The reduced teaching load of teachers in East Asia is important. It means that they have the time to devise excellent lessons and to observe others teach. Of course they have to be able to cope with larger classes – but they do cope, partly by ensuring pupils are well behaved and follow clearly established routines. One reason the pupils behave is that the lessons are excellent so pupils are engaged.


Barnaby Lenon

Finn, J. D., & Achilles, C. M., 1990, Answers and questions about class size: A statewide experiment, American Educational Research Journal, 27.

Higgins, S., Katsipataki, M., Kokotsaki, D., Coleman, R., Major, L.E., & Coe, R., 2013, The Sutton Trust-Education Endowment Foundation Teaching and Learning Toolkit. London: Education Endowment Foundation.

Jepsen, C. and  Rivkin, S., 2002, Class Size Reduction, Teacher Quality, and Academic Achievement in California Public Elementary Schools, Public Policy Institute of California.

Stevenson, H., and Stigler, J., 1992, The Learning Gap: why our schools are failing and what we can learn from Japanese and Chinese education, Summit Books. 

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