Unions also give teachers power to resist changes that make their jobs less fun. I think the teachers genuinely believe that these changes are bad; but I also think that they strenuously resist learning anything to the contrary. There is really good evidence for the benefits of direct instruction in teaching disadvantaged children. But direct instruction moves the teacher into being more of a technician and less of a creative professional. Ian Ayers talks about this in Supercrunchers, giving the example of bank loan officers, which used to be a skilled, prestigious jobs, and are now almost a clerical role. Doctors and teachers are resisting an attempt to do similar things to their jobs through, respectively, evidence based medicine and direct instruction.