Discrimination is always a part of these proms, except, perhaps, in small towns. After a short appearance at the official prom, the graduates separate into groups at private functions.

In Canada, Catholic and "public" high schools are separate (each given its own tax base) so the first separation is on the basis of religion. Another separation (for those so-inclined) is also on the basis of religion, some attending one or more Jewish schools. There was agitation for a Muslim school, but I don't know if it was ever set-up.
Another level is made up of those attending private or charter schools- some of these are "Christian" schools supported by various faiths, other are aimed at higher academic standards (some quite expensive).
My city has over 20% visible minorities. The children of some of these groups will not be allowed to attend school proms by their parents, for religious and cultural reasons.

All of these graduates will have to learn to associate and work with each other but only after graduation.

The U. S. systems have many faults, but I wonder if Canada's "Multiculturalism" is going in the wrong direction.
As I stated before, segregation is alive and well.