Applypie
The children in private schools are likely to do better because
by definition their parents are interested enough in their education to decide to work to pay for it.
Their home environment is also more likely to support learning as the family are investing in it.
The parents will tend to have higher earning jobs, and on average will be more academic than the general population. Their dcs are therefore likely to be on average more able.
Many private schools also select on ability.
There are obviously many exceptions to all these points.
So it is no miracle that the results tend to be better than in the state sector, where there are all sorts of families with widely varying attitudes to education, incomes and living conditions.
Here's the point, the fact that the results of the school are not as good as the private sector does not mean that the teaching is necessarily superior at the private school. It's just that a group of children who are more challenging to teach have been eliminated by selection, whether academic or financial. The remaining group are artificially selected and are pokey to do well anyway.
I have confidence that my dcs can do well in a state comp. The fact that there are children there who are disadvantaged will help them to understand the challenges many people have to face in life, and broaden their outlook. To me, that us an important aspect of growing up and learning to have a part in society