"Not Counted" in student Attendance Summary?

@Daniel Wallach - We take attendance by class. Similar to @Scott Chrysler, we have reasons to keep track of students who are not in class because they are on a school-sponsored trip (athletics, field trip, etc) or are involved in an on-campus activity (Upper School choir performing in Middle School Chapel, etc.) We want to know if a student is actually in the scheduled class or not, but we don't want to count those school-sponsored events against the student's totals.

Using these reasons to keep track of absences also allows us to look at the statistics: overall, did students miss more classes for athletic or for performances or for field trips, etc. Having the info can help us see attendance patterns - or refute assumptions about attendance.