Last year, DD's end-Y7 target for maths was one whole level progress from her SAT L6=6b, but for everything else it was:
(Reading SAT + Maths SAT + Writing TA)/3 + 2 sub-levels
[There are annual national tables for converting between SATs marks, points, fine points and level:sub-level.]
It was mixed-ability for everything but maths. I got the impression all subjects taught their standard departmental lesson plans for Y7 and the differentiation was what it clearly is at secondary: a sham, a vacuous slogan.
Despite that, DD magically achieved her end-Y7 target of two sub-levels progress, no more, no less, in everything but drama. That was even true of maths, where she hit the target of 7b before the end of the autumn term and was banging her head on a 7a assessment ceiling for the next two terms i.e. they "accidently" reduced her overall end-Y7 rating to a 7b they had predicted, but she had long exceeded.
Levels are a crock. They're especially annoying if you've got a whizzy child because that makes it a lot more obvious that they're a crock.