I believe I have persuaded my gung-ho son that a high school diploma is necessary before he joins the USMC. I pointed out that if 50 guys are bucking for promotion, and 49 of them have a high school diploma, who do you think is going to be kicked out of consideration first?
But there's nothing like actual numbers to give reality to a situation.
Thank you for raising a fine young man who wants to serve his country. Has either of you even spoken with a recruitor? I ask because I’m pretty sure the USMC won’t accept him at all without a diploma or GED. They’ll welcome him at the age of 17 into the Delayed Entry Program so he has time to prepare for bootcamp beforehand, but that’s not an automatic “in.”
If he wants to have a say in his choice of MOS - no guarantee there but they DO try to at least get you into your chosen field - he’d better his negotiating platform by staying in high school or, if he’s especially motivated, passing extra credit courses at a CC so as to graduate earlier than his peers.