jeanne I am sure that in terms of university destinations my DDs would have done as well in a local outstanding comprehensive state as in their private school, though possibly not quite as well in terms of grades. That is based on the discussion of the experience of their peers, both in outstanding state comprehensives, albeit with lower levels of social deprivation than average, and private. Class sizes are similar, around 25 in both, but generally behaviour problems in mixed ability state classrooms does mean that private school teachers can take the pupils through the curriculum more quickly and then focus on developing the skills which will get them the extra grades. But the university admissions system, especially Oxbridge, is actually quite effective at levelling the playing field where it is just a matter of the odd grade difference between pupils of equal ability, aspiration and motivation.
However we didn't have the choice of a place at a good state school. That is a common issue in the vicinity of LEH - the state school next door was handed to a Swedish sponsor some years ago which implemented it's educational methods in the face of parental, teacher and OFSTED cynicism and having not succeeded in achieving adequate improvement are now handing the school over to a multi academy trust with the local outstanding schools. The school actually highlighted a mentoring scheme with LEH and Hampton sixth form pupils coming in to mentor GCSE pupils in their improvement plan review as having helped mitigate problems with the recruitment and retention of Maths teachers which was impacting the GCSE years. I am quite sure that that is why the proportion of pupils educated privately in Richmond is at 30% way above the national average and the highest of any outer London borough and that anxious parents of Year 5s and 6s are resorting to tutoring on a level not otherwise seen outside Asia.
And we didn't in any case chose schools because we thought it would get them to a better university. We helped them chose the school where they would be able to get a place in which they felt they would be happy and inspired to learn. In the vicinity of LEH there are private schools like St Catherine's which offer a more nurturing environment with smaller class sizes which is exactly what some families are looking for. For my DDs though it was too small and too mollycoddling, they wanted the challenge and buzz of a school like LEH. Frankly we were never under any illusions that every teacher would be inspiringly effective, some were, others relied on the ability and motivation of the pupils, and some couldn't cope with clever disruptive pupils, but in the latter case the parents were queueing up at the door to complain and in dysfunctional years even LEH will lose pupils and class sizes will go down. As other have said there is so much more to the environment a school provides for the development of individuals than just class sizes.