The most important protection for teachers is the tenure system. As a long time unionist, I recognize the value of collective bargaining on two levels: it saves the job of individuals with capricious administrators and it prevents firing based on the higher salaries of long serving educators at a key point in their preparation for retirement. Even the Final Average Salary calculations of NY and many other states reward long service.
Ironically it also prevents growth. If there is one process that ferments learning other than academics it is travel and the new adventures and experiences that come with it. For journeying broadens the individual and her awareness of the world beyond - beyond the classroom, beyond the immediate environs, beyond an increasingly homogenized culture, beyond the practices of the local schooling system.
Curiously, the business model, so often cited as a better way to structure schooling, does not function in nearly so oppressive a way. We regularly hear about a businessperson being promoted or taking a job at another company or in another part of the country altogether. And often at higher pay. While teachers are deliberately restricted in their salary negotiations so that once seven years or so has been put in, it rarely pays to leave your 'home' district much less leave the state of your previous service unless governments have worked out a beneficial relationship honoring contracts across state lines. Why would you suppose that is? Is this the way to reward and encourage quality educators nationwide? Of course not.
Promotions do occur within a district. They usually require a classroom teacher to become an administrator, or in some cases a counselor. And how many great classroom teachers have become rather ordinary administrators and never return to what they once did so well? We need to re-balance these inequities.