Eiither it is a coincidence that they all have faith doctrine, or the faith bit is important to the attainment.

If the faith bit is important, this needs exploring. The logical conclusion is that God makes you clever?

Perhaps they all have pitched roofs? All have head teachers who drive Volvos? Either faith is an element, in which case why? Or it is a coincidence.

The coincidence bit could be the one actually. If they have the reputation, parents will want their kids there. The parents who want their kids there are the ones who urge their kids to do well, and so it perpetuates.

The trick is not to accept that God looks after his own, but to get all schools to a standard of attainment that is appropriate and for for purpose.

A bit like when the last government introduced choose & book for hospital operations. The dozy buggers thought people would like the idea of travelling far for a better service, when all they wanted was their local service to be as good....