My DD's daycare was totally nut free, and they would throw away anything brought in that was questionable. Now she is in kindy in a public school and we have not been told any restrictions. I am pretty sure there is a \"nut-free\" table in the cafeteria, but there have been no guidelines for the classroom - and each week a parent is designated to bring in snacks every day. When it was my turn, I made nut-free choices out of common sense. But I didn't go out of my way to check if something was processed in a facility that also processes tree nuts. I do know that there is one girl in the class with a nut allergy, and her mother provides her own snack (and she understands that she can't eat nuts). I don't think her allergy is very severe.
At my DD's after school program (she also goes there full-day on days when the school is closed) she told me that if you bring peanut butter, you have to eat in the hall.
One suggestion: could the other student's parents try a peanut butter alternative, like Sunbutter (made with sunflower seeds in a totally tree-nut-free facility)? I think it tastes pretty similar (even better, actually), and if I send a sandwich to school with DD, I always use that, just to avoid any issues.
I don't know why some parents get so defensive about making accommodations like this. It's for a kids health, for pete's sake! What if it was their kid?