Nit picking is not reliable
Nit picking is the most common misguided form of control for head lice among medical and school professionals. It does not work. If it did, there would be no lice left.
Here is the usual scenario: Head lice are discovered after itching. You run to the pharmacy and buy the pesticide based Rid or Nix. You apply it but it doesn't kill all the live lice.* The instructions say to wait 9 days before re-application but you are desperate and get another box to put on. Finally, you think you have killed all the live lice but now you have to get the nits. You pick through the possible thousands of nits. The nurse examines the head and agrees that there are no more nits. However, 2 (or more) nits were missed by both people. Those nits take 14-20 days to hatch. The new hatchlings start eating at the scalp but since there are only a couple of them, they go unnoticed. 7 days later those hatchlings are now reproductive adults and start laying 10 eggs a day. In 14-20 days they all hatch and soon the itching begins. Many people (including the school medical professionals) think that the child has be RE-infested when actually, a couple of nits were originally missed. This is why nit-picking is ineffective.
The National Association of School Nurses and The American Academy of Pediatrics both agree that nit-picking is NOT the answer. Too many children are left home due to no-nit policies. Nit are not the ones that are transmittable anyway, it is the live lice that move.
The National Pediculosis Association SUPPORTS the no nit policy vehemently. However, even though the NPA is a nonprofit organization their administrators get a paycheck from the Association. And one of the main ways they make their money is by selling a lice comb (the LiceMeister comb). I find this to be an incredible conflict of interest and am disgusted by their practices. They operate under the guise of helping children with head lice but actually they are probably con-artists getting government grant money while selling products for profit.
* Rid and Nix are both pesticide based head lice treatments. The Food and Drug Adminstration (FDA) puts a limit on how much pesticide can be put on a human being with minimal safety liabilities. The FDA puts a cap on how much pesticide can safely be put on a human. Rid and Nix (and any other pesticide based product) have a problem because head lice have become immune to the capped amount of pesticide that is considered safe. Head lice are now immune to the levels of pesticides delivered by Rid and Nix. The FDA orders Rid and Nix to put a disclaimer and orders them to put a 9 day wait period before reapplication of the pesticide. This does not hinder desperate caregivers though to ignore the warnings. When the one dose of pesticide based head lice treatment does not work, the caregiver usually goes and buys (and applies) more highly unsafe and dangerous pesticide levels on (usually) a small child. DO NOT USE PESTICIDE BASED HEAD LICE TREATMENTS!