Yes teachers unions and associations exist to protect teachers. Unions are also just collections of teachers, an issue with teachers unions is an issue with unionized teachers. Often what's good for students are usually good for teachers. Teachers unions have been known to fight for smaller classrooms, less of a focus on standardized testing, and greater support from specialists for students.

Teachers ability to organize is one of the few benefits and source of almost all of the benefits that attract people to the profession. Just compare education in states that have teachers unions and ones that don't. They better serve students.

Beyond that, what teachers or union says that schools are for anything but the education of students? What initiatives that would benefit students have unions prevented?