All I can say is, when I was in grade school, lo, these many years ago, no one wore costumes to school on Halloween and frankly didn't expect to. Putting on costumes was done before we went out ToTing and was looked forward to with excitement and impatient anticipation.
We did make decorations for the classrooms, as we did every month for whatever holiday applied, which we entirely enjoyed. I certainly did not feel deprived because the schools did not have a party or costume parade for Halloween, and I think I grew up quite unscathed