Don't go into teaching if...

1. You are anti-intellectual. You can't expect your students to do more (like go to college) if you can't even cut it.
2. You are willing to wait for the worst kids to drop out. There are some kids that are difficult to get motivated etc. but they have their reasons and you waiting for them to just drop out is a disservice to the time they do spend in school.
3. You think that age is equal to experience. Students have experience, many of them very different than the experience you probably have but a lot of experience none the less and every experience (or even apparent lack thereof) is an experience.