I’ve been told by friends of mine who teach general studies in very Yeshivish schools is that the classes are touted as not important and therefore the students are less likely to take the teacher seriously. Also, the principals don’t back them up because its just general studies classes and not Judaic studies.
I don’t know if this is true. I do know, that when I was in elementary school, we were definitely meaner to the non-religious or non-Jewish teachers. Although, we were rather mean to a teacher right out of seminary when I was in 5th grade and basically ripped her to shreds. So maybe kids just feed on weaker teachers.