You could upgrade your tank and have some fun projects for the kids (what age group do you teach?) with some diy learning activities. A couple ideas:
1. Making a gravity ATO is a relatively simple project and just needs an empty container of some sort and a bit of airline tubing. If you have older students you can build your own sensor based ATO (much more complicated)
2. Brine shrimp hatchery (tons of how to’s online)
3. Phytoplankton culturing and/or copepod culturing
4. Refugium build
5. Surge systems (might be a bit too noisy/messy)
6. Doser build (this would require more expense for the pumps and older kids)
7. Auto feeder
most of these projects use things like empty 2 liter bottles or a used (hopefully free) small aquarium and a bit of airline.