You do not need to know all of this to get into grammar school! My dd goes to a super-selective and their tests are not based on this type of stuff (which you can drill if you start early enough) but more on verbal/non-verbal thinking (e.g. spotting patterns in shapes and language), creative writing and so forth.
I agree that a good understanding of language structure is helpful for learning languages, but as others have said, if that's the case, they need to start this very early on in primary, as it takes a while to build up this type of knowledge.
I don't think it's realistic for many children to be scoring well on this test though- yes, the bright ones will, just as they do well in the ridiculously hard spellings now having to be covered, which again most adults in the population fail. All that happens is that the minority of bright kids get good grades, the majority don't and just carry on into secondary with really quite poor literacy and grammar because they didn't 'get' it in the way that the government laid out or on that timetable. It doesn't actually change base levels of knowledge if you set things to be really difficult so that only a minority do well!