I was just talking to a friend about this yesterday. He married a woman with a 16-year old son, brought up with no male influence. Needless to say, the boy is a mess. I suggested turning him over to the military when he comes of age to see if they could turn him around.
Depending on how much of a mess, and any redeeming features the kid has, they may not want him. The military of today is lean and mean. They don't have the time,nor the resources to be messing with spoiled mama's boys, or girls for that matter. If the kid really wants to join, that's one thing, but a kid who doesn't want to be there is probably going to be a waste of the investment in time and resources that it takes to make a solider, sailor, airman, or most especially a Marine.
The more redeeming features, an aptitude for language or the ability to learn to maintain and operate the complex equipment the latter particular important for would be airmen or sailors, can offset some minor behavioral problems. But it won't offset a criminal record, even a juvenile one.
Bottom line, you have to raise your kids, don't expect Uncle Sam to do it for you.
That said, the judgment of parents, particularly step parents, as to the worth of their kids is not particularly good. It can off either way, but when it's off in the low direction, it's often way off.