Do class sizes have an effect

Do class sizes have an effect on student learning?

Because of the coronavirus pandemic and the resulting health advice, lack of staff and social distancing measures, schools have had to adjust their class sizes accordingly. But does this mean that smaller class sizes are here to stay? And what’s better for the overall development of children?

The current state of class sizes

“Class size is defined as the number of pupils in a class with one teacher. Average class size represents the average number of pupils being taught by one teacher during a single selected period in each school on the day.” (DfE, 2011)

Over the last decade or so, hundreds of thousands of children up and down the country have been taught in classes of more than 30. In fact, it’s become increasingly common to have larger primary school classes.

However, the most recent statistics (January 2020) suggest the “average class size in all primary schools decreased slightly from 27.1  in 2019 to 27.0 in 2020. The average class size in all secondary schools increased from 21.7 in 2019 to 22.0 in 2020.

The impact of class sizes

A new piece of research that compares classes of 17 with those of 23 asks, ‘Do small class sizes improve student achievement in primary and secondary schools?’

Published by Peter Blatchford and Anthony Russell at the UCL Institute of Education (IOE), Rethinking Class Size covers the follow themes:

  1. Differentiated teaching is more difficult
  2. Reduced knowledge about pupils
  3. Classroom management more demanding
  4. Reduced amount of activities
  5. Increased demands of marking etc. and,
  6. Increased teacher stress.

The relationship between class size and pupil outcomes

“The most obvious way of investigating the effect of class size on pupil attainment is to examine the association between class size on the one hand and some measure of pupil academic performance on the other,” note the authors.

Somewhat surprisingly, studies have found that pupils in larger classes tend to do better than those in small classes. Even so, the results are “hard to interpret” because the relationship between the ‘independent variable’ (in this case class size) and the ‘outcome’ (pupil achievement) can be explained by another, confounding factor. Those factors are:

  1. Relatively poor-attaining pupils tending to be in smaller classes;
  2. Teachers are forced to change their style of teaching in larger classes;
  3. Experienced (and possibly better) teachers are assigned to larger classes.

Countries and regions at the higher end of the attainment chart, such as Hong Kong and Shanghai, have relatively large class sizes, meaning this variable may not make a difference on student outcomes.


As explained in the research project: “The effects of class size on academic outcomes are clearest with the youngest students in school…Class size is important for older pupils, but that the effects are not so obvious and not necessarily direct.”

The use of teaching assistants may bring advantages to the classroom, but their negative impact on academic progress doesn’t mean this is the answer to large classes.

Also, the project found that there was “more pupil on-task and less off-task behaviour as class sizes decreased,” and “less on-task and more off-task behaviour as class sizes increased.”

Comments for this post are closed.