Schools in Israel are not allowed to send kids home if they are infested. So they can tell and beg mothers to check their kids’ heads, but can’t enforce a clean head policy. So that means that those mothers who do care have to regularly check and comb their kids’ hair to avoid infestations. If knits or bugs are found, a few very thorough combings with a fine tooth comb and lots of conditioner does the trick, without need of poisons and chemicals, which often don’t work 100% anyway.
In American, I know schools where they check heads in school and send infested kids home and do not let them back in until they are clean, so spreading infestations is less common.