They force the kids to have a Cinco de Mayo celebration? Do they serve discounted Coronas in the lunch room as part of the festivities?
I ask because I've never heard of anyone observing that day other than going to a Mexican restaurant.
Dude, great deals on Margaritas on Cinco de Mayo.
Seriously though, I don't think "force" is an accurate term. In school, Cinco de Mayo is an opportunity to wear crazy clothes and eat lots of candy (provided you bring your own these days of course) and even have a class "foreign food" party. We did Cinco de Mayo at my schools, and I haven't turned particularly Mexican.
What becomes a problem is when they build up these other cultures' holidays but ignore or run down traditional American holidays/events in American history. For example, when learning about the constitution, focusing on the 3/5ths compromise and many Founding Fathers owning slaves instead of the fact that America revolutionized (no pun intended) political thinking in the Western world towards liberty and "natural rights".