It's normal for kids to "enjoy" something without wanting to "practice" it. I would suggest you get the teacher to comment that he doesn't seem to be progressing and he won't get to play fun stuff unless he practices the routines designed to develop his hands, fingers, coordination plus learning the positions for the various chords. The teacher doesn't have to say you told him - the teacher can just ask your son to be honest about how much he's actually practicing since the teacher isn't seeing the results. Remember that the teacher gets paid whether the kids practice or not, so they aren't likely to suggest that someone quit. But if you tell the teacher you may not continue if the kids doesn't want it, maybe a word or two will motivate your son.
From there, give him a week to practice as directed - and that means 20-30 minutes (or whatever is recommended) of straight practice - not counting snacks, bathroom breaks, phone calls, etc.! He will see progress at the end of one week if he does this.
If he still doesn't, then stop the lessons for a while and see if he really wants to go back to them after a 2 month break.
A lot of kids think that guitars, in particular, are really cool - and they want to be rock stars. They don't realize that rock stars WORK!
But I don't believe in throwing good money after bad if the kids are just squandering it. We live in a society that wants instant gratification, where often practice is considered unfair. Don't buy into it.