wix.com is a free website builder, but he isnt going to learn to actually do anything other than drag n drop, as far as website building goes. It would give him practice writing and some sort of design stuff maybe. But no code.
Well...there might be some coding in the background if you can get into that in wix, I honestly havent tried it out (But I do know it's legit).
Another one I would recommend is wordpress - you can get a free blog there and it would be similar to setting up a website.
https://en.wordpress.com/signup/