She's teaching kids something with demonstrations.
Having middle school kids lie down on the floor doesn't really demonstrate anything. Nothing really wrong with it but still unnecessary and doesn't really convey any educational meaning. But this part?
When one of the students said she felt fine, the teacher then put her foot on the girl's back and said "How does it feel now? See how it feels to be a slave?"
That's not only unnecessary but also kind of fucked up. Not in a "white lady stomping on black kid" kind of racist way, but more of a "get your fucking foot off of that kids back" kind of way. I'd be pissed as hell if that was my daughter's teacher. You don't tell kids to lie down and put your feet on them.
From whatever perspective you look at (racist or just unnecessary) this lady is an idiot and should be reprimanded appropriately.