How old is he? My boy says he wants to continue, but damn is it hard to get him to try anything new or to practice outside of his lessons. I just learned that his instructor has been introducing chords to him...I sat him down and tried to do some work with him on the chords I knew he had learned. He seemed to have no interest in it and wanted to practice the riffs he had learned weeks earlier.
He's 17. I don't tell him anything, he's always practicing his chords. He's a bit of an overachiever though (he's a Junior at University of Florida!). Ask me in a year if he's still playing though.
My 2¢ on kids and stuff like this: Don't let him quit, but let him do the parts he likes. If you push too hard, he might ditch the whole thing. I have two older kids that I forced through piano lessons for several years, but later allowed them to choose, and they quit. Now all of us regret that - they wish they had continued, and I do too.