I would switch up the treatments, never use the same one as they can get use to it.
It also doesn't help when other kids at school do not get treated and you are doing the treatments for nothing really so make sure to tell his teacher/school so they can let the parents know there has been an put break of head lice and for parents to look out for them on their children etc.
We deal with nits all the time at work.
Everything from capes, combs, clips, scissors, clippers, towels needs to be sterilized for health and safety.
2 hours in hot initially boiling water with a disinfectant.
Head lice can't live off the scalp for a very long time, but still follow this as the larvae can live longer than the adults and if you have just treated some adults can re-attach and start the cycle again.
It's a PITA.