That size tank would be fine for an ATB but probably too small for GTP and ETB. However ATBs tend to sleep all day and usually lay in a hide or coiled up on the ground so they don't make for an impressive display (during school hours at least).
It looks like you were already moving on from those ideas but I just wanted to add those $0.02.
Another idea that might work is a giant day gecko?
Good luck!