Odds are full face makeup isn't allowed. Most of the time, full face makeup isn't allowed on school campuses because it may make it TOO difficult to identify a person in an actual emergency. All it takes is one person who ISN'T supposed to be on campus, and the school can go into complete lockdown. Full face makeup or coming to school with a full-headed mask on, especially on a day when masks, costumes, and props are expected to be in large numbers, would make it really easy for someone to get on campus unnoticed.
I'd go with something partial, something with stripes or splotchy patterns but still showing skin. Definitely no zombie or all-black paint.