This question seems to get asked a lot around here, lol.
I've only had one type of fish legitimately school in an aquarium and they were feeder guppies. They were acclimated to saltwater over a couple of months during a fallow period. I originally purchased 100 guppies with the intent to convert them to saltwater. It worked - they survived the transition. What they didn't survive was every other fish in the tank. They lasted a few months in the tank until they were all picked off by other fish.
As just about every other person on here will tell you, it's nearly impossible to get fish to school in a home aquarium. Shoaling is common, but a lot of people are looking for the schooling effect. Feeder guppies are the only fish I can think of that stay small enough, you can buy in large quantities for little cost, and will legitimately school in your aquarium. The only question regarding these fish is whether it's worth it to you to have to acclimate them to saltwater over time; to have them school for a couple of months or so, and then do this process all over time and time again?
One caveat, when I started returning fish to the display after the fallow period, the guppies went in first. They did not school until the other, larger fish were returned to the display. If there's no legitimate predator then there's no legitimate schooling.
Another side note - guppies are not the strongest swimmers around. A high flow reef tank may cause the guppies to hang out behind the rocks or in lower flow areas.