M.D.
My home tested high for radon at the home inspection. The seller installed a mitigation system. Afterwards, the radon levels were undetectable. We've lived here for 15 years now. We have it tested periodically to make sure it's still working. Levels have been below the detection limit every time. So, I can say with confidence that a mitigation system works. And none of us have lung issues.
I don't know the answers to your other questions (schools, etc).