Any study that shows that is complete and utter total crap. I know that to be a fact from the education I personally received in the U.K. It would have been simply impossible for me to have achieved the qualifications I did aged 16 if I had been taught in mixed ability classes.
Explain to me how being grouped in maths class of clever students that where able to speed through the curriculum take the exam early and then speed through a Statistics O level ending up with two qualifications instead of one those in the "fast" maths class I did worse than if I had been in a mixed ability class and only done the standard mathematics O level? You can't it is utterly impossible for me to have done better being in a mixed ability class.
Repeat for a fast science class where instead of three hours a week for each of biology, chemistry and physics the clever students had the option of doing each in two hours a week and fitting another option in.
The result is that by streaming/tracking I was able to achieve 10 good O level results compared to the standard which was 8.
People who think that not streaming children results in better results for ALL children are in fact complete MORONS. Anyone who has done a study that proves that clearly failed to take a statistics qualification at some point because my *SINGLE* example disproves the cherished educational theory.
These are the sorts of MORONS that result in the William Tyndale scandal
Yes I know all about this because my parents who where both teachers visited the school at my Aunt's request where she was a school manager.
Back when I was doing my O levels (last year that did them before they became GCSE) this was a widespread practice at good schools in England and Wales (Scotland has a completely different school system).
I can also clearly remember my school days *BEFORE* we hit the age where streaming was introduced. I remember being extremely frustrated at the slow pace of the lessons for years.
Clever children do better if they are streamed, and holding clever children back so they can pull other people back is completely unacceptable.