Well, you've got a point there, schooling is a behavior, but numbers do matter. Two neons in a tank will not show much in the way of schooling behavior, there just have to be more fish. Now, if you've got two goldfish, a much more sociable fish, they will exhibit more "schooling" tendencies.
Anyway, in a tank, without a natural predator, you're more unlikely to see true schooling. I have a 55g with almost 90 cardinals, and while there is a mass of color and movement, it is not schooling. It is just a lot of fish in a small tank.
Val