Ok so who could have let them in that would be "authorized". If the school board member has a key (and I really don't understand why he/she would have had a key in the first place), then that person is authorized to unlock the door and have access to the school and as such, he/she allowed the students that same access.
What these kids did was harmless. The punishment is ridiculous.
Winner, Winner, Chicken Dinner! (That just seemed appropriate for this thread.) As a student, I felt quite confident that any adult in a leadership position at the school (teachers, principal, parents on the mom/dads club, coaches, etc.) were "authorized" to give me permission to do things. If they weren't, they let me know who I was supposed to ask. I can't begin to imagine why you think an entire school board would be involved with giving permission for someone to be on school grounds. Could you imagine how that would work? "Hey teacher X, I know it's after hours, but you're still here and you have a key, would you mind if you let me in to school so I could go grab a book?" "Sure Johnny, I'm happy to help, but first let me call a session of the school board so we can obtain proper authorization to be on school grounds."
As an adult, I wouldn't even think to question that. If a teacher at my kids school has a key and lets me in, I think it's quite reasonable for that to constitute permission for me to be on school grounds.
As a total aside, I think I finally just noticed that luvmy3 and luvsjack are two different posters, which makes sense because I have totally been confused by some of your responses on other posts that just didn't seem like something you would say! The luv must have been throwing me off...