Well, the problem is that school budgets routinely get cut quite aggressively, and from an administrative standpoint, it makes sense to get rid of the teachers who have been there longest; they're drawing the largest salary, so they're the obvious choice. School administrators don't really see "better" teachers as having a higher ROI, so it's a good cost-cutting measure to replace your highly-compensated teachers with younger teachers who will work for less money. This obviously has a detrimental effect on the quality of the education, but it rarely costs administrators their jobs. The problem is that tenure doesn't just protect good teachers who cost a lot of money, it protects bad teachers who cost a lot of money; it's not merit-based, it's experience-based, and more experience doesn't automatically make someone better.