As easily countered with emprical data to prove that the "progress" expected is not accurate. :)
Ofsted’s claim – that children who achieve top grades at primary school should go on to achieve top grades in later exams – was challenged as inaccurate and unrealistic by new research published on Wednesday.
"Rebecca Allen, director of Education Datalab – a specialist education statistics startup – said its research showed the majority of pupils did not follow linear paths for academic attainment but instead showed considerable movement.
“It simply isn’t reasonable to assume that a child who gains a level 5 [at key stage 2, in primary school] should go on to get an A or an A*,” Allen said.
According to the research, only one in 10 pupils make predictable progress at each stage, while most children will perform better or worse than their expected attainment on one or two occasions."
Also the head of the organisation you are quoting, opposes grammar schools.
Bleddy love Mumsnet and its confirmation bias.