Saving Private Ryan etc.
I do think the teacher should get permission from the parents first.
But, outright banning of R-movies is ridiculous, even if they may be shown to 16-year-olds instead of 17 or 18.
And that's my whole point.
I would not show Saving Private Ryan to a high school class.
My mom cannot handle movies with graphic violence. Some people cannot handle movies like that. You shouldn't force it on them.