UPDATE 31 AUGUST 2015
A recent Daas Torah ruling is compelling schools to accept children who have not been vaccinated against childhood diseases. The decree states that it is contrary to Halacha to prevent children from attending school, even if they hadn't been vaccinated. It was promulgated by leaders of Lakewood Yeshiva and distributed to boys and girls schools in that city.
It quotes Rabbi Chaim Kanievsky who forbids schools to turn away students who have not been vaccinated.
Rabbi Harry Maryles writes in Emes Ve-Emunah (Friday August 28 2015);
Schools cannot deny enrollment to unvaccinated students. But schools may or even MUST deny enrollment to students with Internet at home / long hair / blue shirts. So to recap, parents who risk the physical health of an entire school are cool. Parents who are merely perceived as risking spiritual wellbeing of others are not cool."