As readers of this blog will know, I regard the imposition of a grammar test at key stage 2 as mistaken, without basis in research and fills the curriculum with even more stuff that takes time away from children getting a chance to find out what kinds of reading and writing they might really like to do.
However, I'm realist enough to know that what has to be done has to be done.
With this in mind, I'm going to suggest one approach to the teaching of grammar that you can take and run with, adapt and use as a basis for thinking of other creative ways of playing with grammar.
1. Take a several passages of written text and chop them up into single words. End result a huge bank of bits of paper with single words on them.
2. Put the children into pairs or groups and get them to make up some writing.
3. Share what they've made round the class. Do they make sense? Do they sound 'right'? If they don't, discuss what would make them make better sense?
4. Play the substitution game. What happens if you swap single words over? What if you take out just one word and find another word to take its place? Can you do that? What have you got now? Read those out. Do they still make sense?
5. What the children have done here is 'do grammar'. They have taken the aspect of language that runs along a line (phrases, sentences and paragraphs) and made some out of the random pile of words you have given them. They will nearly all do this 'grammatically'. If they don't, others or you will make suggestions as to how they will work grammatically. This is if you like the 'grammar that is in the children's minds' which they learned between the time they were born and they were about 5 (leaving aside for the moment the question of whether they are 'first language English speakers' or not.
6. When you asked them to play the substitution game, you were treating language as 'vertical'. You were replacing one kind of word with another word of the same kind. By doing this you introduce the children to the notion that there are words of one kind or another. Words have categories. They both know this and don't know this. This is one way for them to make their knowledge explicit.
7. You can do this by first getting them to come up with names for the categories that they have just demonstrated. Or you can introduce the names that are conventional - 'noun', 'verb', 'preposition' etc.
8. Go back to the occasions when people made sentences that didn't 'sound right'. Or get the children to make up sentences that don't sound right. Or make up some (still using the words on the bits of paper) and see whether they can come up with reasons why they 'don't sound right'. What should they be?
9. You will almost certainly now be dealing with 'word order' (the most easy aspect of English grammar to pick up if you are a 'native speaker' but hard even for very experienced speakers of English like, say, football managers!) You will also be dealing with eg 'subject-verb agreement'. This is the way we make the 'verb' tie in with the 'subject' of a sentence. As you probably know, for many children they do this one way when they speak which is different from the way standard English does it. That's why it's difficult for them. So some London children will say 'we was'. Some Yorkshire children will say 'he were'. Standard English, as you know says 'we were' and 'he was'. You can 'teach' these things by telling children how to write it, you can get them to do exercises. I'm suggesting here that you may well find it more efficient, more fun and more intellectually satisfying if you play with these 'constructions' using cut-ups (words printed on to bits of paper), and getting the children talking about the different ways of saying and writing these constructions.
10. Invent other ways to investigate and play with language rather than doing exercises.