They could (i) send a letter to all parents (ii) get their cleaners to pay attention to the bogs and (iii) ensure that teachers send the children to wash their hands each and every time they go to the toilet, eat or come in from the playground. Teachers need to stand in the cloakrooms to ensure that proper hand hygiene is observed. That's how you get rid of the bloody worm problem.
You can worm the Boy until you are blue in the face but unless he washes his hands as described above (as a minimum requirement) it will do no good.