"J.D., JD" does have a nice ring to it! In truth, I agree with you. If you don't have the drive to do it, law can burn you out in no time. Not all lawyers make the "big bucks", but most work long and hard trying to. If your heart isn't in it, don't go there. You mentioned the shortage of qualified math teachers, that probably is more of an advantage for HS level than earlier grades. It's not easy to find qualified teachers for trig, calculus and statistics.
After you get the regular teaching certificate and have a few years worth of good references, try to get into a private or religious school. Why? Because the kids there generally want to be there, and the parents care enough to send them there. You won't be dealing with as much of the apathy that runs through a public school student body. That's the main reason private schools have such good graduation and college admission rates: kids who want to be there and parents who actually give a damn about education.