Found a cool macroinvertebrate key here.
If you teach biology, you likely teach your students how to use a dichotomous key when you discuss classification/taxonomy. This could be used for such an activity. Or, if you teach some sort of aquatics, ecology, or environmental science class, you might have your students use it to help them identify macroinvertebrates from pond water samples (checking for the presence of different types of macroinvertebrates is a good activity to teach them how to gauge the health of water ecosystems).
Anyway, check it out!