So basically in an average state school all of the lower set and half of middle sets gets zero grades 4 in English and Maths.
The thing is, given the way the exams are set up, isn't that exactly what you would expect?
The percentage 'allowed to pass' is essentially set, and then the pass mark is decided. So in 2018, just under 30% got lower than 4 in each of English and Maths - because that is EXACTLY how the exam system was designed.
The question is whether you would expect the high overlap found between the c. 30% who don't get level 4 or above and those who leave primary with low prior attainment (which for those taking GCSEs in 2018 meant they got less than a 4 in KS2 SATs in 2013).
In 2013, 14% of children got less than a 4 in KS2 Reading SATs, 15 % in Maths, 17% in writing.
Would you EXPECT that a statistically significant proportion of children who were in the lowest 15% in primary after 7 years in school would be above the 30th centile in attainment terms in the same subjects after 5 more years? Yes, of course there will be some individuals - children who were relatively recent arrivals in the UK later in in primary, for example; children whose SEN were diagnosed and better managed in secondary; children whose individual circumstances(e.g. bereavement, illness, family circumstances) happened to be very difficult in 2013 but better 5 years later. But would you expect there to be a large enough number to affect national-level statistics?
I would expect, by the way, for there to be a different picture for subjects other than English & Maths - because performance in Maths / English at KS2 is not a good predictor of success in GCSE Art, for example.
Why do 'Well above average' state schools achieve slightly differently for their low prior attainers? I wonder whether that is to do with circumstances other than school, and also the way that low prior attainers are distributed between schools demographically. So in a school with a very small proportion of lower attainers, each may well receive much more individual attention, which is simply not possible where these children ate 35% of the cohort. More importantly, we have all been arguing here as if the only influence on pupils' results is school and in particular the teacher. Some low attainers will be in that group at the end of primary, and at the end of secondary, because of family and personal circumstances - worklessness, chaotic f familes,addiction within the family, poor housing, very poor parental levels of education, gang involvement etc etc. As 'well above average' schools are often - not always, but often - 'sought after', they will tend to serve catchments, or socio-economic groups, which have a slightly smaller proportion of these 'children affected by issues outwith the school's control, and this may mean that the school can create more progress for children whose lower academic attainment is 'simpler' than it is for those where it is compounded by social factors.