I'm afraid, being deeply cynical, I think this is entirely about not wanting informed parents on several levels.
Politically it's rather inconvenient to have informed parents pointing out the new academy isn't doing better than local LEA schools.
Politically it's rather inconvenient pointing out that socio-economic background of schools is linked to performance - that might well be why the new performance tables quintile system has school performance related to 'similar schools' - I rather suspect performance in Richmond if directly compared to Selly Oak would see St. Mediocre in bottom quintile instead of middle.
Locally - I think this is about taking the pressure off teachers. If parents aren't seeing school work (which has been widely introduced in Birmingham - literally nothing comes home and only a small selection is available at parent/ teacher meetings)/ no books are coming home/ little or no homework coming home and the evaluation of pupil performance is radically different (maybe oranges to apples/ hedgehogs to antelopes) between Birmingham schools - why there's no local pressure on a failing school to 'buck up'.
Like many things - I suspect the political necessities behind this move to decentralise schools and 'marking' - is entirely about putting parents in a position where there is nowhere to complain. LEA's are without power and gradually being undermined with the establishment of non-LEA controlled free and academy schools. Schools only have to establish a system - they aren't required to convey that system's meaning particularly clearly.
It will go badly wrong somewhere. There will be an enquiry. There will be embarrassing headlines/ reports on tv & the usual wailing and gnashing of teeth. There will be the statement in parliament about how more rigorous standards need to be in place - but can we just spare the expense and go for a one size fits all system (oh like the NC Levels we're just abandoning - which lets face it are so broad that parents don't really twig 4c is not ideal and 4a is solid but not outstanding).
Teachers are increasingly afraid of parents. And I suspect that's because parents are increasingly frustrated with obfuscation/ games being played in relation to our children's education - which in fact we care about a lot.
Teachers/ Teaching unions have agreed these changes as well - and that's because it also suits them not to be terribly clear with us PITA parents who have the temerity to actually want to understand where a good pupil should be by this or that point in school.
For all of Gove's belly aching wanting higher standards - I don't see him insisting that NC L5 is the new benchmark of primary progress at end of KS2 - yet 45% or more pupils achieve this (see data end of guardian report on KS2 2013 attainment: www.theguardian.com/news/datablog/2013/sep/19/sats-results-key-stage-two - where in 2013 48% of English pupils achieved NC L5+ in English (including SPAG)/ 41% achieved NC L5+ in Maths).
If we were to think of this as ye olde fashioned bell curve - why a high NC L4 (high 4a)/ low NC L5 (so low 5c) would be on the 50th percentile and would translate (using old school system) into A BIG FAT C (which used to stand for 'middling performance'). The reality is the government/ teachers are quite simply deeply unprepared to be that blunt about it.