Honestly? I wouldn't send my child to a school where vaccination rates are below herd immunity levels.
The meaning of "vaccines aren't 100% effective" is that they may not work in a very few people or they may not provide complete protection in some people. The personal risk to a vaccinated person is low. However, a vaccinated person may have a mild-ish cold-like illness that's actually measles (or something else). This person can spread the disease to someone who's very vulnerable (a young infant or a person who can't be vaccinated for medical reasons). The 3 infants who died of measles this year were all too young to be vaccinated when they contracted the disease. This is really serious stuff, and again, our schools are failing badly by not teaching it.
The thing is that it's very easy underestimate the risk of disease and overestimate the risk of vaccines. Many people see conditions like measles and mumps as being benign diseases of childhood. They're not. Measles almost killed my sister in the very early 1960s (she developed encephalitis). Before vaccinations, it killed, literally, millions of people every year and left permanent damage in many more.
So no, I don't think that (personal belief) unvaccinated children should be allowed to attend school, public or private. Medical exemptions are different, which is why everyone else needs to be vaccinated: herd immunity protects the ones who are allergic to the components of the shot or who have another problem precluding vaccination. The risk the unvaccinated people pose to (many others) is simply too high.
