If there isn't a threat to the school, they'll go wherever they want. Add a predator and any schoolers will bunch up.. Safety in numbers, and all that.
:iagree:Rasboras are definitely up there as a tight schooler as well. My rasboras are never apart.
This makes perfect sense but I have to say that my rasboras are always together, never are they at all ends of the tank. They are always in a group together. Now I've only got a 10 gallon so that may have something to do with it.