People can't spell at all nowadays. I know high schoolers who can't spell "cinnamon." I know middle schoolers who cannot spell the word "accusative" when it is on the sheet in front of them.
I know we have spell checkers now. But they can't catch everything and they are not an excuse for mental atrophy. At some point, everyone is going to have to go outside that format, and if he can't spell worth a damn, he is screwed.
People like to tell you that spelling is a talent and not a skill, and therefore one shouldn't be censured for being a poor speller. This is garbage. Spelling can be improved by hard work and practice, and it ought to be. You are doing no one any favors by allowing him to spell badly. He will come off in later life as illiterate and uneducated and, guess what? He is.