Ultimately, the SPaG test (Spelling, Punctuation and Grammar test for 10/11 year olds in English schools) was NOT introduced for reasons of giving children opportunities. It was introduced because it was deemed to have 'right and wrong' answers. This, the argument went, would enable the examiners to grade the children 'accurately'. In turn this would enable the DfE to grade the schools 'accurately'. In turn, this would enable the DfE to determine more 'accurately' which schools would have to be compelled to convert to academies, even though there is no evidence that conversion will make the school better.
So, in a way, none of this is about 'grammar' and everything to do with creating academies, i.e. giving 125 year leases of publicly owned property to private companies and charities.