Finally, haha I was just about to clarify this myself. Too many people use these words interchangeably.most freshwater fish in the hobby are shoaling fish, forming a loos aggregated network. Schooling fish are fiarly tightly and work more as one unit.
Although i dont have experience with them, it seems that most people agree on rummy nosed tetras as the tightest schooling fish group. there are other fish which work great and are more colorful but they might not form real tight aggregations.
My Congo Tetras shoal fairly tight, but they are slightly bigger than what you're looking for. Rummynose tetras are excellent for what you're seeking though, as is a nice sized group of cardinal tetras.