I second 1077. At least six of any tetra species will mean less stressed [= healthier] fish.
When you say "school with" it could mean two different things. First, most tetra will not "school" with other species, except now and then; the species that are schooling (or more correctly shoaling) tend to remain together. But the second meaning could be compatibility, and any non-aggressive tetra will be compatible with Pristella.
However, here you should research the fish thoroughly. Pristella are more active than some, and do like a bit more water movement. Black phantoms are quite the opposite. If the tank is spacious, say 3-feet long or more, this can work as the Pristella will remain closer to the filter outflow and the Phantom at the opposite end. Look for active swimming tetra species. Or perhaps small danio, those there is not a lot of different colour in the danio. Neon Tetra
would do well with Pristella.
Any of these need a group of 6 minimum. You can get more ideas in our fish profiles, second tab from the left in the blue bar across the top of the page. Look under characins (for tetra) and cyprinids. Each profile includes information on activity level, water filter needs, etc., and of course compatibility.