Without getting into the whole "you spoiled brats back in my day we never went on senior trips" rant (JK)
Seriously, it depends on what hotel you are staying at, and where you do it.
From my perspective, take the following examples, all during the day:
1 - Only 1 pool at the resort, and you were all congregated around it - I would probably be a little po'd, especially if (since you are in togas) you aren't swimming. Go somewhere else
2 - At a multi-pool resort, you guys go for either a smaller, or more out of the way pool - that would actually be okay with me. Even if we stayed right there, it would be more like any other time when the pool is busy - "well, we'll just walk to another one!
3 - Multi-pool resort, you guys go for the main pool - I would personally not care, because we don't like the main pools anyway
but I can definitely see where others would be angry.
Basically, my advice (echoing that of others):
1 - Call the resort ahead of time, let them know your intentions, and honestly say you are willing to accept their decision. The best way to make a good impression (especially as a group of "children", yes I know you aren't but that is how they may see you) is to submit to their authority.
2 - Try to have the chaperones or some designated "peacekeepers" there - I know you all have the best intentions, but it only takes one shove, or one person to bring a flask and get drunk, and you may have a problem. Have someone there that can "handle" the situation before it gets out of hand.
3 - Most of all, be kind and courteous to other guests. Don't block walkways, don't run past them when going to and from the party, and most of all don't get cocky when they complain (because they will complain, i'm sorry but that is the honest truth - people will complain).