Legally he can drop out at age 16 in MO with a parents written permission, but if thats not given there is no way around the issue. At age 18 he can do what he wants, but I still think it's a bad idea. The level of education keeps increasing year by year, and not having a highschool diploma will not get a very good job. Even a GED still looks bad. I am sure your son knows this, but he just hasnt thought the desision through and that is why he can't give you a solid reason too. I'm sure he will change his mind, just keep after him telling him how this is a bad idea. Good luck Don!