Education historian Diane Ravitch, writing about the Chicago teachers strike, but has lots of relevance across the board
What do the teachers want? The main sticking point is the seemingly arcane issue of teacher evaluations. The mayor wants student test scores to count heavily in determining whether a teacher is good (and gets a bonus) or bad (and is fired). The union points to research showing that test-based evaluation is inaccurate and unfair. Chicago is a city of intensely segregated public schools and high levels of youth violence. Teachers know that test scores are influenced not only by their instruction but by what happens outside the classroom.
The strike has national significance because it concerns policies endorsed by the current administration; it also raises issues found all over the country. Not only in Chicago but in other cities, teachers insist that their students need smaller classes and a balanced curriculum. Reformers want more privately-managed charter schools, even though they typically get the same results as public schools. Charter schools are a favorite of the right because almost 90 percent of them are non-union. Teachers want job protection so that they will not be fired for capricious reasons and have academic freedom to teach controversial issues and books. Reformers want to strip teachers of any job protections.
Encounrage you to read the whole piece, here.