When you go to a new school, you should be able to watch a class. If they will not let you watch an entire class, go to another school. If an instructor has a good attitude, the students will, too. In order for the class to be successful, the kids have to enjoy what they are doing. They also have to enjoy each other.
Some schools offer a trial period.
This is a good alternative to a longterm contract because it offers you the chance to see if you like the school. The instructor should prove himself to you. If the instructor is not good, you can walk out. When I have the opportunity to sign a new student, I could fast-talk his parents and get them to sign their kid up for a year. I don't want to do that.