When a junior high school student in western Oregon tested positive for the coronavirus last month, Sherry McIntyre, a school nurse, quarantined two dozen of the student’s football teammates. The players had spent time together in the locker room unmasked, and, according to local guidelines, they could not return to school for at least 10 days.

Some parents took the news poorly. They told Ms. McIntyre that she should lose her nursing license or accused her of violating their children’s educational rights. Another nurse in the district faced similar ire when she quarantined the volleyball team. This fall, after facing repeated hostility from parents, they started locking their office doors.