What is it?
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 receive will increase, improving outcomes for students.
How effective is it?
Reducing class size appears to result in around 3 months additional progress for students, on average. Intuitively, it seems obvious that reducing the number of students 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 substantially, such as to below 20 or even below 15 students. It appears to be very hard to achieve improvements from modest class size reductions above 20, for example from 30 to 25.
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 students 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 achievement can be 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 primary school).
There is some evidence that reducing class sizes is more likely to be effective when accompanied by professional development for teachers focusing on teaching skills and approaches. Some evidence suggests slightly larger effects are documented for lower achievers and, for very young students, those with lower socio-economic status.
Smaller class sizes may also provide more opportunities for teachers to develop new skills and approaches.
When used in isolation, the reduction of class sizes in Australian schools has little effect on student achievement. Rather, pedagogy must also be transformed alongside smaller class sizes. Nevertheless, there remains little Australian-based research on how to instruct teachers to adapt their teaching practices for smaller class settings.
A 2014 study from Macquarie University used international test data to assess the relationship between class size and achievement. The authors concluded that there is not a strong relationship between class size and learning. A 2005 review article by Professor John Hattie noted that, in Australia, it has been difficult to find studies linking lower class sizes to increased achievement.
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 students in smaller groups. Overall, there is a relatively consistent finding that smaller classes are associated with slightly higher achievement when other factors are controlled for and when class sizes have been deliberately reduced in experimental evaluations.
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 reduced to 15 students or fewer. Cost estimates are based on the employment of an additional teacher however the impact of this on class size is variable. For example, the employment of an additional teacher with a year group of 50 students would enable two classes of 25 to be split between three teachers with either 16 or 17 students in each class.
What should I consider?
Small reductions in class size (for example, from 30 to 25 students) are unlikely to be cost-effective relative to other strategies.
Reducing class sizes for younger children may provide longer term benefits.
Smaller classes only impact upon learning if the reduced numbers allow teachers to teach differently. Have you considered how you will adjust your teaching strategies and what professional development will be required?
The gains from smaller class sizes are likely to come from the increased flexibility for organising learners and the quality and quantity of feedback the students receive (see Feedback). Have you considered how you will organise learning in smaller classes and how you will improve feedback to your students?
As an alternative to reducing class sizes, have you considered changing the way you deploy staff (both teachers and teaching assistants) so that teachers can work more intensively with smaller groups (see Small group tuition)?