In terms of progress 8 scores, some of our local schools are feted on the basis of good scores in this measure. How is this measured for pupil intake from schools that don’t have KS2 data? And surely a good score in any particular school, particularly a Grammar school, could simply be a reflection of a lower underlying intake standard too? I can understand why it’s a useful measure for comprehensive schools, but I would not have expected the grammar scores to be as high? Or perhaps I’m misinterpreting it...?

What happens at our grammars is those without SATs data are compared to the data of children entering who got the same score in the 11+ exam.
So if say a child scored 330 in the Nonsuch and Wallington 11+ those without SATs are compared to the SATs scores of the girls who also got 330.
There has to be some baseline as they get expected progress grades right from the first school report.

Thanks Moon unit.

From the Government document about secondary measurements including progress 8:

“There will be some pupils (those arriving at secondary school from the independent sector or abroad) who have no key stage 2 results to use as the baseline for the Progress 8 measure. These pupils’ scores will not be included in the Progress 8 measure. “

Source: https://assets.publishing.service.gov.u ... th_ref.pdf

When you look at the fine details on the compare schools tool of number of pupils who took exams and number included in measure it can give a rough guide of those who were not previously at state primaries. Some of course may have been removed for last term of Y6 so as said just an indication but an indication nonetheless.