Teachers make up one of the largest single segments of the American work force—as of 2010, there were approximately 4.2 million kindergarten through 12th grade teachers in public and private schools. Very generally, teachers' unions are labor unions that represent the needs of those teachers, as well as other education-related workers like day care employees, K-12 paraprofessionals, and professors (in selected areas). These unions receive dues from members and have the power to negotiate on behalf of those members as a group and defend their rights from capricious action by the management—which, in the case of teachers, is usually the school administration. Theoretically (and often practically), this collective bargaining unit allows the teachers to use their large numbers and threat of a strike to garner ...