Believe me there are many stress relieving benefits, its my therapy, and I love it. If anything the kids will learn a thing or two, obviously if they solely focus on it then they need to be diciplined, maybe have a 5 min viewing when class starts so they get it out of their systems!
Any class that had reptiles or animals I personally always focused and did better in those classes!
Hope this helps! For those interested HABRI (Human-Animal Bond Research Initiative- www.habri.org) compiles peer-reviewed research relating to human/pet interaction. I think they have a couple research papers on the effects of aquariums/fishkeeping on human health and well-being.
That is too bad that they are wanting you to get rid of your tank. The power argument is pretty weak. The average school uses $180/student/year in electricity. If you have 300 students your school's power bill is probably around $4500/month. Your tank probably uses in the neighborhood of $5/month or less, less than one tenth of a percent of the total usage.
I work at a small rural K-8 and I have a 300 gallon in the entryway of our school (Common Snapping Turtle named "Snappy") and a 125 community tank in my 4th grade classroom. I feel very lucky to have coworkers that appreciate the tanks - I have almost always had a tank in my classroom.
Tucc185 mentioned petsintheclassroom.org - they are a great resource, I've received $200 in grants from them since last year!
Anyways, good luck and be sure to let us know how this pans out.