Many schools have rules against using them. It is difficult to get enough trials to make the results reliable. You also may need permission from a veterinarian. On the other hand, if you do want to work with gerbils, go for it.
Gerbils are one of the cleanest friendlist classroom pets available.
In terms of biological rhythms, find a way to observe your gerbil's activities. If you do not have such a camera, you could set up an observation schedule in which you or someone else checks on the animal every hour for a few minutes. Watch him for several days. Then, put him in an environment without any time signals. In other words, close off the windows and turn off all lights.