Do smaller primary classes get better results? 14,315 schools say no
Answer: Smaller primary classes did not have better results in this national school-level comparison. Among 14,315 mainstream primaries, schools averaging 30 or more pupils per class recorded 68.1% FSM-adjusted RWM attainment, versus 55.2% among schools averaging under 24.
That is a paradox, not a recommendation. It would be a serious mistake to read these figures as proof that adding pupils to a class improves learning. The more likely explanation is selection: popular and advantaged schools fill their classes, while small schools can be rural, shrinking or serving communities with different needs.
FSM-adjusted primary RWM attainment by average class size
| Average class size | Schools | Raw RWM | FSM-adjusted RWM | Average FSM |
|---|---|---|---|---|
| Under 24 | 3,930 | 54.2% | 55.2% | 28.7% |
| 24–26.9 | 4,060 | 61.1% | 61.7% | 27.3% |
| 27–29.9 | 5,182 | 65.1% | 64.4% | 21.8% |
| 30 or more | 1,143 | 70.3% | 68.1% | 15.6% |
Why does the raw result run in the “wrong” direction?
The under-24 group averaged 28.7% pupils eligible for free school meals; the 30-plus group averaged 15.6%. That intake difference explains part of the raw 16.099999999999994 percentage-point attainment gap. We removed the simple linear relationship with FSM share and the gap narrowed, but it did not reverse.
Other unmeasured differences remain. Average class size is partly an outcome of demand, school size, geography, staffing and admissions. It is not a random treatment. A national cross-section cannot isolate what would happen if the same pupils and teachers moved from a class of 23 to a class of 30.
What should parents look for instead of one class-size number?
- How teaching is organised. A headline average can hide very different year groups and subject arrangements.
- Whether additional adults are deployed well. The one-teacher class measure does not capture every teaching assistant or specialist intervention.
- Stability. Sudden changes in class organisation can matter more than whether the average is 27 or 29.
- Your child’s needs. SEND support, behaviour, teacher quality and classroom routines can outweigh a small numerical difference.
Frequently asked questions
Do smaller primary classes get better SATs results?
Not in this school-level comparison. Larger average classes were associated with higher RWM attainment, even after a simple adjustment for free-school-meal share. That does not mean large classes cause better results.
Why might larger classes appear to perform better?
Popular, high-attaining and urban schools may fill classes more completely. Small rural schools, schools with falling rolls and schools serving higher-need communities can have smaller averages for reasons unrelated to teaching quality.
How many schools had at least one class over 30?
6,660 schools in the matched analysis (46.5%) reported at least one one-teacher class above 30 pupils.