Is a union the best answer? In reality, I think we need to look at other options.
One thing I have always thought about is setting up teacher education. Those that want to come can and those that do not do not come. The class is run by experienced teachers and can be on a variety of subjects ~ depending on what the teacher feels they have enough experience in. It’s not a formal teacher training program that will leave you with any sort of qualification. You will just have more tools in the toolbox when you take a seminar.
Making yourself a better teacher and having the parents see improvement in your students, they will want to stay in your classrooms. This is, of course, assuming the school is good.
As far as working for bad schools that do not care about the kids, I think that is part of the learning curve. I did that for 3 years in Taiwan before finding a good school. Not every process is perfect there and I am not claiming to be a perfect teacher, but it is nice to be able to help students that need it, communicate the challenges you see with students to the parents, and present a plan on how to change that. When parents see that and they see measurable results, they love it. That requires an experienced teacher. A school that has teachers coming and going every year will NEVER achieve that.
As far as the teachers are concerned, those that have a good school, improve their teaching, keep the students coming, and add new ideas will ultimately be able to get a better salary from the schools they already work for when it’s time to sign the new contract. Through the contacts in the group, people will know what jobs are good and which jobs are shite. As people go home or move on, they will be one of the first to hear of openings.
Let the natural selection happen where other schools either close or get the teachers that are not here long term.
Sorry if this post is not organized at all. It is late. I am exhausted and I zoned out on the TV a few times. I did not proof read this…deal with it!