Size determined by performance
OFSTED could have said more. There is actually a positive association between class size and exam results - the bigger the class, the better the results: even better from the Government's point of view. But this is not evidence that the former causes the latter.
The reason is obvious to people who work in schools - pupils who are slow learners are usually put into smaller classes while high-fliers are often in quite large classes.
The class size is determined by the performance, not vice versa.
Statisticians are aware that association is not the same as causation: the Government and OFSTED need to realise it too.
If you invert cause and effect, it is not surprising that you get nonsense.
JOHN BAUSOR Education consultant 5 Longcrofte Road Edgware, Middlesex