P'sNeedle: it's one of the rarely discussed advantages of streaming. I know on these boards it is 'streaming bad, setting good ' but with enough flexibility, deployed because a good comp actually wants the right education for each child, it works well.
After all, a Grammar school is essentially streaming. The advantage of the grammar stream being in a comp means that all children can move in and out of different level classes.
Basically they are in streamed tutor groups. From the off. Music, Geog, history, PHSE , all subjects except maths, English, science and languages are done in those streams, and then maths etc are set. Many children are set across strams, there is carefully considered movement, and children move streams, too, especially late developing summer borns, or those who want a very vocational path into the BTecs.
It is a comp which is known for doing well by childen of all NT abilities, and not in a well-to-do inflated house price area, either.
I fully agree that childen with special needs need a specialist provision in terms of much wider experience of staff, specialist facilities, different scale etc.
Units for childen with emotional issues, behavioural issues, sensory disabilities, ASDs etc all work well, from what I have observed, and free childen to fulfil their potential. General 'grammar area' selective seems to do the opposite , trapping the numerical majority of childen in a school where they may not be able to take 3 MFLs, because they 'failed' the 11+, or leaving a grammar child struggling at the bottom of a bottom French set, losing confidence in a high pressure environment, because there is no middle set to move to.