Hey,
Mine always schooled as a species. I had a school of Cardinals and a school of White Clouds. Both tetra's, but they kept to themselves. Again, ask your lfs person because certain fish like the lower 1/3 of the tank, some the upper 1/3 and some go all over. You would probably want schools that didn't necessarily stay at the same level all the time.
Again, if I remember correctly, Cardinals and Neons will school together since they are so alike.
HTH,
Dan'l