Actually, I want to re-emphasize a comment made above. Schooling/Shoaling is a defense mechanism -- when you are in the place most tetras are in the food chain, it is the ONLY defense mechanism. Point is, I think that so long as you are providing a good home, you'd actually want to see your fish NOT school/shoal because that tells you they are comfortable in their surroundings. You want to provide a lot of plant cover or wood or rocks or some form of plenty of places to hide. Diffuse the light some.
Recently I bought a school of threadfin rainbowfish. They schooled tightly for about 3 days. After that, I saw the bravest ones poking their noses into different plants and holes in the wood. Within a week, they were all over the place. They only 'school' now when it is feeding time (or they think it is feeding time). In my mind, that tells me I've given them a home they consider safe.
Maybe I am misinterpreting it completely, I don't really know. I would someday like to get a really large tank and get like 100 fish of the same tetra species and see how they act. It is really neat to watch the schools of 100s or 1000s of fish in places like the Shedd aquarium in Chicago.