When withdrawing a student who is not coming back next year, use a date outside of the School Year overall dates.

For example:
  1. Go to Core > School > Years & Terms
  2. If 2014-2015 has a begin date of 9/1/2014 and an end date of 8/31/2015. You would use a withdraw date of 9/1/2015, this will keep the student's third trimester grades from dropping.