Besides having the "profesional package", you need to communicate to them that you understand their needs as a school, namely safety, reliability and appropriateness. Eg. You have insurance, abide by standard trade practices (safety wire for lights, tape up cables, safe noise exposure) You have a backup system should something go wrong, running 2 amps, circuit breakers that kind of thing. This one is important, you in your contrAct have early termination terms for you and them. Eg if you can't do it, then you have to make it up to them. And that you have appropriate music that will keep the kids and teachers happy, eg no swearing, not overly aggressive no overt sexual themes, yet fun and danceable. That's my 2c.