'it should be about providing high quality education for all that maximises the opportunities for individuals to reach their full potential. In my view this requires a range of educational institutions that have clear & compatible objectives and can focus on being excellent in their respective areas. '
This exactly what the Grammar/ Secondary modern system claimed to do. It didn't.
The problem is selection. How do you do it, when do you do it, without disadvantaging whole swathes of children?
One of the ways you don't disadvantage children is by keeping them in the same educational establishment until the late developers and those born later in the year have had a chance to catch up. The view of Manchester Grammar School 50 plus years ago eg. was that it took approximately to age 15 for this to happen.
For this reason it was decided that a comprehensive school offering broadly the same sort of education to all to 15/16 would be appropriate. The point of a school system is to open up new horizons for children not to keep them confined in any system of disadvantage they may start with.
By mixing up children from all backgrounds a true comprehensive school benefits everyone. It shows those from educationally poorer homes what is on offer and shows those from more advantaged homes to respect and understand those less well off than themselves. A win win situation.
Children who play together, learn together, work together are less likely to have weird ideas about people who start from different places than themselves.
We have learned, haven't we (?) that dividing children artificially on grounds of religion ( Northern Ireland) only prolongs the divisions in society. Dividing children on spurious grounds of educational aptitude is no less dangerous. It leads the 'chosen' to think they are superior , more worthy of having their opinions listened to; that others are 'not like them', don't need the things they need.
It leads those who are not chosen to carry chips on their shoulders for years, to lack confidence, to think they are unworthy of consideration, that they are for ever pressing their noses up against the window but never being able to take part.
By all means offer options after 16. Anyone who has taught knows that unfortunately it is only after 14/15 that many children start to leave behind them their adolescent bad behavior and become more mature and able to make considered choices.
For this reason I am against too much choice before 16 as it gives pupils an opportunity to miss out on very important subjects and therefore subjects that may limit their future.
The real problem in our schools is funding; especially for staffing. Our local prep school has approximately 12 children in each class. Virtually no state primary school can do that across the board. Many schools are still desperately short of books, facilities and equipment. It is not because state school pupils are without talent ( see Jessica Ennis) that they didn't feature as much as private school pupils in the Olympics. It was that they didn't have the chance.