What is so special about primary/secondary teachers that means that teachers with tenure are automatically better to retain than those without? If it's really a better system, shouldn't all employers base their promotion/firing decisions on seniority rather than merit?
I work at a job where I am promoted over more senior people if I do well and will be fired if I do badly. While the company is far from perfect at judging, it still does a much better job of choosing who to retain/promote than mechanically basing it on seniority. I can't imagine how we'd benefit by saying that we can only fire employees that are new (instead of ones who are unproductive) and that our best employees would be permanently stuck behind the more senior ones. In fact, I imagine we'd go out of business.