I've worked in both state and private schools. My observation with my own dc (in state schools) is that those who are very able academically could be given better opportunity to excel, but aren't. I see it as a great shame.
It seems like in order to tick the 'inclusive' box or help those who need more support, the children who are more capable aren't really given very challenging work.
An example would be that my dd is put in a very mixed ability group for maths and English. However, previously the class had different tables depending on level of work - those most able were given more challenging work. Those less able were given less challenging work. I've now been told by the teacher that this wasn't 'inclusive' enough for the slt. Apparently my dc is learning through 'coaching others'. I think she should give a higher level of work to those most able, I'm not interested in my dc 'coaching others' when she could be learning more complex work.
Private schools seem to have no issue with streaming children. Perhaps I've just been unlucky, ultimately it doesn't matter as I help my children learn at home, but what about capable children who don't have home support?