Even if the fear mongers are right and wifi microwave radiation is carcinogenic (ok, no proof of that but let's just say there is for a moment) then banning wifi in schools is not going to stop other wifi radiation from entering the schools from neighboring buildings.

I love my mother dearly but she had the same concern at home when I suggested my parents get wifi a few years back. I pointed out that if I turned her laptop on she could already see that there were 4 wifi base stations emitting microwave radiation that was passing through her brain anyway. So not getting wifi wasn't going to stop any risks (if there were any).