We have gone in October twice and only saw one high school group and it was at the MK. We did have a couple of international tour groups though....one from Brazil in 2007 and one from Mexico in 2009.
I know that when Pop Warner goes to Disney in December, they usually stay at the Values and CBR.
Depending on the reason the group is there, they will most likely be up and out by 9:30am at the latest.
We ran into the high school group and the group from Brazil at the MK, and the group from Mexico at DHS. When we stayed at ASMo in December 2006, we only bumped into the Pop Warner kids twice - once in the cafeteria in the morning and once at Epcot one night.