There are lots of resources available to your son.
I agree electronic spell checkers are a waste of time. Type in peel, and you find out that, yes, it is correct. Well, okay, but not if you are talking about the sound a bell makes.
However, a spelling dictionary is really useful. You can look up the word "giraffe", and it will be listed in red letters as, "jirafe", say, with the correct spelling next to it. There are definitions next to the correct spellings, so you know you have the right word.
By year 7, could he be typing a lot of his homework, at least? That way he can use the spellchecker on the word processing software. It's much easier to edit using a computer, anyway, and even if it has to be handed in typewritten, he can type it up, then copy it out, which is no different from doing a rough draft and final draft, anyway.
DD2's Y7 English teacher told her off for spelling "dyslexic" incorrectly. Makes you laugh, really. Or cry.