White House black tie guidelines?

[Tobus]

my usual approach to this sort of thing;
"It's easier to ask forgiveness than it is to get permission"

The problem with high school prom is that they will likely turn him away at the door if he doesn't meet their dress code (assuming they enforce it rigidly). So it's not like he can get away with it and then ask forgiveness later. He will either have to get permission first, or be refused admission.