I think this depends on the other animal experiences that you have. If you don't have anything else, you can break your time in school up into species or class, for example. If you have other (more valuable) experiences, I would do your best to give them their own space and cram your high school experiences into one spot. If you think about it, a lot of things you did were probably very similar across species - handling, feeding, etc. Again, this depends on what you already have and if these experiences are "more valuable"/better quality.
For me personally, I grouped things generally by where I worked with the animals. Even though I've worked with a bunch of different species at the lab animal facility I'm at now, I lumped them together and mentioned the species in my blurb as well as what I did (feeding, handling, injections, health checks, etc) for all of them.