Head lice should be taken seriously, and addressed by teachers and parents promptly. If your child's school has a head lice problem, school administrators have a responsibility to notify parents and make sure kids that are infected are sent home so the lice can be properly treated.
If you feel that the school isn't handling the situation properly, I suggest you first talk to the administration, and then someone at the school district level.
Below, I'm including a link to a Head Lice Information Center. It contains helpful articles and tips for getting rid of head lice.