The way we do it is only for actually being IN class during the event. We had some fraternity philanthropy events scheduled for weeknights when girls were in class, and it would be wrong for them to skip class for it. "I need to study" is never excused, since you have the calendar of events in advance and need to manage your time around it. Girls could still skip events for things like that but it was unexcused and counted against them. Sorry if that wasn't clear :)