A good dance school is a positive place to be and work in. Anyone that is going to be attending the school should be able to benefit from a positive environment, then. If you are unsure of the environment and are worried it isn't positive sit in during a session.
When determining if a dance school is the right one for your child, consider how well the dance teacher interacts with your child and you. Are they patient, willing to work individually with children? Do they understand the body? Do they encourage or do they seem overpowering? This can help you to determine their level of skill.