I haven't had to do too much of this while in school nursing but from my experience during nursing school
while working in the nursing home:
1) Have lots of wipes handy and already out of the container. It's difficult to get them out sometimes without having to constantly change gloves. Also, even though the wipes are technically ready to use, it sometimes helps to wet them a little more with warm water.
2)Tear pullups down each side and remove like a diaper instead of trying to pull them down like panties/underwear. Just kept things a little more "contained" rather than streaking it down their legs.
2) If there is a bar in there (like in wheelchair accessible restrooms) I'd have them hold on to that and lean over so I could see/reach the need to clean areas better. With kids who might be a little more steady on their feet, if there is not a bar ask them to put hands on knees or reach for their toes.
3) Make sure a trashcan is handy and easy to use. Sometimes it's difficult to put trash in a lidded trashcan quickly when your gloved hands are soiled.
Our school only has pre-K special ed and the teachers/parapro's generally handle all toileting with these kids. I do know they have a special changing table with little steps so the kids can climb up which helps save the backs of those working there. If you are assigned this job, I really think you should petition for some kind of changing table. I'm not familiar with older kids in this situation though, so I'm not sure what the norm is for that area.