Among academic circles in education and the teaching associations, properly executed mixed ability is very highly regarded, as it is in all the schools in which I have worked (most of whom have never done it) because local schools which did it were so successful and well reputed.
Yet wandering around in cyberspace are a number of people who hate it.
I had to teach mixed ability secondary maths between 2006 and 2008 because I worked in small school heading for closure in particularly unusual circumstances. I was very lucky in that some some highly skilled teachers came out of retirement to teach me how to do it.
It is indeed a very strong way to teach with unexpected benefits both for students' progress with maths and for their personal development into being, in general, more confident, mature people who are more at ease in situations where they don't know exactly what to do or what's going on mathematically.
Personally I'm a yin and a yang kind of person. Given the choice I would put perhaps a couple of terms of mixed ability into year 8 and perhaps a term at the start of year 10 now we're on linear maths GCSE with terminal maths assessment. Naturally I'd make sure the teaching plans and objectives for those terms were very clearly understood and explained to and by all involved.
The question I'm asking today is
"Why is there such a strong will to deny the existence of/discredit those great teachers who were so highly respected and who inspired me?"