The original question had to be edited down. The recent Chicago Teachers' Strike, which stopped education for nearly half a million children, helped to illuminate what are valid reasons for demonstrating against institutional injustice. Using this as a blueprint, I think that some very good points can be made as to why there is a need for teachers to go on strike.
The first reason to justify demonstration via strike would be to protest the way in which teachers are evaluated. In a growing response to scrutinize the job teachers are doing, evaluation models that are simply impossible to enforce or where success is beyond challenging are imposed on teachers. Teachers should be able to retain some level of voice as to how they are being evaluated and assessed. In order to sustain long term growth and professional reflection, employees should have a voice in the construction and development of their evaluation frameworks. Indeed, teachers are fighting for the same. A common misperception is that money is the number one issue teachers go on strike. I think that the evaluation model is as important, if not more, in terms of a reason why teachers would consider going on strike or demonstrating their own resistance. Any model of evaluation that does not take their voice into account can be seen as reason enough to protest.
Another point to make as to why teachers would demonstrate dissent by going on strike would be to protest working conditions. In the modern classroom, this comes down to class size, air conditioning and heating, and even textbooks. There are some basics that any workplace must feature in order for employees' effort to be maximized. Teachers fight for reduced size in classroom, as instruction can be more effective with smaller sizes in class numbers. While there is evidence to suggest the opposite, I think that any teacher would say that they are more effective with a class of 21 as opposed to 31 students. At the same time, I think that classrooms have to have basic amenities such as proper heating and cooling in order for teachers to teach and for students to learn. Finally, the Chicago Teachers' Strike, raised an issue that did not get much in way of publicity. Many Chicago Teachers have to wait six or seven weeks in order to have textbooks in their students' hands. It is difficult to gauge the effectiveness of instruction when materials and resources are not delivered in a timely manner. Providing these in an educational setting is a part of the work conditions standard that could sway teachers in demonstrating by going on strike.