If a vaccinated teen is exposed to meningitis at school, will they get it?

It depends: on the type of meningitis. Most teens are vaccinated for meningococcal meningitis and some for hemophilus influenza B and pneumococcal, but if it's viral meningitis or a different bacterial meningitis, they are not protected and could get it. Also the vaccine isn't 100% effective and there is a booster recommended at age 16 (initial one usually done at age 11).