Harry, in the DH epilogue, reminds his son going off to Hogwarts to not duel till he learns how.
Why didn't Harry teach him at least the basics by that point? He was already 11 (?), so old enough to learn the rules and some very simple spells (Hermione "tried simple spells" before she even got on the train, and she was from a Muggle family).
Given that he would attend together with Scorpius, Harry ought to have taught him SOME basics.