How old are you? If you're still in college, go for SAT for sure. You don't want to be teaching MCAT to your college classmates; it really undermines your authority if you are taking college classes along with your MCAT students. At the same time, you're just the right age where high school seniors will look up to you. But if you're a non-trad, then I'd advise you to go for MCAT. You have enough of an age difference that it's not like you're teaching your peers, and as you get older, you eventually reach a point where you lose your cool factor with the high school set. 😉
When I started teaching, there was no training. Now the training generally lasts for five sessions (post audition). Whether you get cut or not depends on your trainer and on how short-staffed your center is. It's definitely possible for you to get a few extra training sessions if they think you have potential but feel you're not quite ready to handle a class yet. Conversely, you could get cut after one or two training sessions if you're not getting with the program, so to speak. My advice is to put the time into prepping well, because blowing your homework off is the surest way to get yourself cut quickly. You need to work that hard to prep your actual classes, too. Once you take over an actual class, you will find that the students constantly keep you on your toes. MCAT in particular is very challenging, because you are getting asked tons of science content questions, and you need to know the material cold. Think of the most annoying gunner pre-med you know, and realize that he and all of his friends will be students in your MCAT class. If you're not prepared, they'll be completely merciless. I've seen new instructors teach one class, leave, and never come back.
