What is it?

Reducing the number of pupils in a class. As the size of a class or teaching group gets smaller it is suggested that the range of approaches a teacher can employ and the amount of attention each student will achieve will increase.

How effective is it?

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. However, overall the evidence does not show particularly large or clear effects, until class size is reduced to under 20 or even below 15.

The key explanation for this appears to be whether a 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 have been identified, in addition to improvements on behaviour and attitudes. In some studies these benefits persist for a number of years (from early primary school through to at least the end of Key Stage 2). It appears to be very hard to achieve improvements from class size reductions above 20, e.g. from 30 to 25. 

There is some evidence that reducing class sizes are more likely to be effective when supported with professional development to learn and develop teaching skills and approaches. Some evidence suggests slightly larger effects are documented for the lower achievers and those from the lower socio-economic status for very young pupils. Additionally teachers may potentially further develop their teaching skills and approaches in a smaller class.

How secure is the evidence?

There are a number of issues in interpreting the evidence about class size as many countries or schools already teach lower attaining pupils in smaller groups. Overall there is a relatively consistent picture where smaller classes are associated with slightly higher attainment (when other factors are controlled for) and when class sizes have been deliberately reduced in experimental evaluations. 

The strongest evidence comes from research into primary schools in the USA where the benefits appear to be sustained for 3-4 years when classes are reduced below 18. There is some evidence that pupils in disadvantaged areas in the UK benefit from classes of fewer than 20 pupils in primary schools.

What are the costs?

The costs associated with reducing class sizes to a level where a significant benefit is likely are very high. The evidence suggests that typical classes would need to be halved to 15 pupils or even fewer. A class of 25 pupils with 50% of them receiving free school meals would be allocated an extra £8,000 under the pupil premium in 2012/13; this would not be sufficient to appoint an additional teacher. In 2013-14, a year group of 60 pupils where 50% were eligible for the Pupil Premium would increase funding by £27,000, enabling two classes of 30 to be split between three teachers with 20 pupils in each class. Costs are estimated as very high.