The United States-based National Pediculosis Association recommends that all schools and child-care centres adopt a "No-Nit" Policy. With this policy, children with head-lice are not allowed to return to school until the lice have been removed. The NPA believes we need families to understand that shampooing with pesticides is not enough (and not recommended) and until we manually remove all of the live lice/nits, we will continue the cycle of lice infestation and the cost and suffering that goes with it.
Other organizations, such as the National Association of School Nurses (again, in the U.S.), do not recommend a "No-Nit" Policy. They do not feel that children should miss school over a condition that is not a health risk - especially since we do not have strict policies that keep children home when they have with contagious health conditions, such as colds or bacterial/fungal infections.
I'm torn. Most parents I meet in my business are upset that their schools are seemingly not taking head lice seriously. They are mad at the parents who do not take the time to remove the head-lice from their children and frustrated that they are sending their now nit-free children back into a classroom of infected heads. However, as a working parent, I know it is not easy to drop everything and make arrangements to deal with head lice. If a parent doesn't have the knowledge or resources that they feel they need to deal with the problem, then the head-lice problem will continue. And you can't keep a child out of school for too long.
Also, having nits does not automatically mean that you have lice. There was a study where 63 children were found that had nits but had no bugs. Over time, only 18% developed cases of full-blown head lice. So, with that research, a no-nit policy seems a bit excessive.
My thought is that schools should do regular head checks, through the school nurse, or through volunteers, or through professionals. Schools should equip parents with the best information regarding head-lice. Precautions should be taken to keep coats from touching in the coat room and costumes should be regularly laundered. Students should be encouraged to keep their long hair tied back and all kids should be regularly reminded that they can't share hats or combs. The school should be a place where parents and kids can talk about head-lice without denial or shame. If you are an educator, let's talk about how we can do this.