As the size of a class or teaching group gets smaller it has been suggested that the range of approaches a teacher can employ and the amount of attention each student will achieve will increase.  So, intuitively, it seems obvious that reducing the number of pupils in a class will improve the quality of teaching and learning, for example by increasing the amount of high quality feedback or one-to-one attention learners receive

But Professor John Hattie revealed in his book “Visible Learning” that class size doesn’t  really matter that much .  Or rather, his research  showed that on a list of factors that affect student learning class size mattered the least, which is not quite the same as saying it doesn’t matter.

The average size of a class taught by one teacher on the census day in January 2014 was 27.4. Overall in England, there are more than 58,000 Key Stage 1 classes (pupils aged five to seven) of which almost 3,000 had at least 31 pupils in them about 12 months ago. So, although the number of students in classes with more than 30 children has trebled, we’re still only talking about one in 20 classes across the country.

As Professor Justin Dillon points out ‘One of the reasons why class sizes have risen is that there are more primary-aged children now. Since 2010, the number of Key Stage 1 pupils has risen by 11.2%, but the number of classes has only grown by 8.1%. The coalition government changed the rules on admissions – meaning, for example, that schools have to accept pupils whose parents are in the armed forces or who move into an area where there are no surplus places.’

In the US, a team of researchers randomly allocated pupils and teachers to one of three types of class within the same school. The three models were: “small” classes, which had 13-17 pupils; “regular” classes (22-25 pupils) with just one teacher; and “regular” classes which had a teacher and a full-time teaching assistant. The project involved more than 7,000 pupils in nearly 80 schools. The pupils were followed through four years of schooling, from kindergarten (aged five) to third grade (aged eight). Pupils in small classes performed significantly better than pupils in regular classes and gains were still evident after grade 4, when pupils returned to normal class sizes

The Education Endowment Foundation, here, says of class size ‘ overall the evidence does not show particularly large or clear effects, until class size is reduced to under 20 or even below 15.’ It continues: ‘The key issue appears to be whether the reduction is large enough to permit the teacher to change their teaching approach when working with a smaller class and whether, as a result, the pupils change their learning behaviours. If no change occurs then, perhaps unsurprisingly, learning is unlikely to improve. When a change in teaching approach does accompany a class size reduction (which appears hard to achieve until classes are smaller than about 20) then benefits on attainment can be identified’

Surveying studies on class size in the US , the author Malcolm Gladwell observed that although really big classes are a problem, there is a happy medium, and smaller classes don’t necessarily lead to better outcomes. This, he explains, is because teachers don’t usually adjust their teaching style to smaller class sizes; instead, they just work less. So, the “disadvantage” of moderately big classes isn’t one after all.

When Malcolm Gladwell talked with teachers about class size he found there was general agreement that large class sizes can impair learning. However, he also discovered that teachers believe that the same is true about small class sizes. Teachers agreed that when classes became too small the group dynamics in a class became difficult, and individual students were more easily able to dominate the group and disrupt learning.

Based on this, Gladwell suggests that the relationship between class size and achievement is actually not linear (as class size goes down learning goes up), but is best represented by an inverted U curve. As class size is reduced, learning improves until the optimum class size is reached. However if class size drops below the optimum learning declines.

Andreas Schleicher, of the OECD, says that  it’s a myth that small classes raise standards. He argues that “everywhere, teachers, parents and policy makers favour small classes as the key to better and more personalised education.” In contrast, he argues, high performing education systems invest in better teachers and high performing countries (many in East Asia) have large classes – so the size of a school class can’t be important. But PISA studies are not dedicated studies of the impact of class size but secondary analyses of data collected by others at just one point in time.

In England, Peter Blatchford directed the Class Size and Pupil Adult Ratio project which, instead of setting up an experiment, simply studied what went on in normal classrooms. Blatchford and his team followed more than 10,000 pupils in more than 300 schools. The pupils were tracked from when they entered school aged four to five-years-old, until the end of primary school, aged 11.

In this study Class size made a difference – children did better in smaller classes in both numeracy and literacy during their first year in school. The effect was greater for the pupils who started school with lower attainment. At the end of the second year in school, the effect was still evident in literacy attainment but not numeracy. Yet by the end of the third year the effects were far less evident in either numeracy or literacy. So, the evidence suggests that smaller classes benefit pupils in their first years in primary school but the effect seems to disappear as students get older

 Blatchford says in a blog ‘ What is needed to address the causal effect of class size are dedicated studies with strong research designs, which deal with the problem of potentially confounding factors, like pupil and teacher characteristics. Two main studies do this, each using a different approach: the experimental STAR project from the USA (pdf), and a large scale longitudinal study in the UK (CSPAR [pdf]). These studies show that smaller classes do have a positive effect on pupil progress especially in the first 2 or 3 years of schooling. Recent French research has found similar effects.’

To reduce class sizes you have to employ more good teachers and reduce the pupil teacher ratio. This all has a very significant impact on educational resourcing-so  it is vital that we are clear about the reliability of the evidence on the effect of class size.

What is clear is that high-quality teaching is the single most important school-based factor determining how well pupils achieve. Class size certainly, at the extremes, must have an effect. Ask any teacher and they will tell you its easier to teach a class of 15 than a class of 35.   But it can also be a nightmare teaching a class of  8  demotivated, disruptive pupils and a joy teaching 40 pupils   who really want to learn.

But reducing class sizes is expensive. And so the question is ,are there  other interventions that are more cost effective, having a greater effect on student outcomes. The answer to that has to be yes. (Hattie et al) Another interesting question is, what would be the effects on student outcomes if   the best teachers taught , larger classes and the weakest teachers ,progressively, the  smaller ones?

A final word to Blatchford ‘:  I think the most important educational questions are about how to adapt teaching to make the most of having fewer (or more) pupils in a class. It amazes me that there is next to no research which evaluates the benefits of class size changes along with specified changes to teaching, for example, the introduction of collaborative group work, which might well benefit from smaller classes.’

Look out for the work Blatchford is doing with the Leverhulme Trust, on class size



  1. There’s something really important here about how the findings of Hattie (and others) should be used.

    The tendency might be for educational leaders to think “Apparently smaller classes (and ability setting) don’t improve the outcomes of pupils, therefore we shouldn’t waste money and efforts on these”

    But the real picture seems to be “Smaller classes (and ability setting) don’t improve the outcomes of pupils, because teachers don’t capitalise on the clear benefits which they simply MUST offer!” (OK, I know ‘must’ is a strong word, but there are some things so bleeding obvious, we just can’t turn our back on them!)

    I’m willing to be shot down on this of course.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s