Over at TNC's place, Cynic marvels at the American education system's perverse incentives:
We want teachers who demonstrate perseverance coupled with ambition, steady improvement over time, and achievement, without succumbing to complacence. Our school systems, on the other hand, are bastions of stability. They extend the promise of steady employment in a volatile world, substantial job security, and for those who stick it out for long enough, an enormous deferred payoff in the form of benefits and pensions. If we'd designed it from scratch, we would have struggled to produce a system more perfectly designed to attract young people who value stability, or to repel and grind down those who seek constant change.
...Work environments hospitable to continual innovation tend to have relatively low barriers to entry, and relatively low barriers to exit. Schools invert that. Many have extensive up-front credentialing requirements, forcing novice teachers to invest substantial time and money at the beginning of their careers, before they can even decide whether they are indeed well-suited for the job. Early career teachers tend to get the least desirable assignments, and to be paid barely enough on which to live. On the other hand, most compensation packages are grossly back-loaded, offering lock-step seniority raises and substantial retirement benefits. So it's tough to get in the door, and once you do, leaving entails abandoning the rewards for which you've already labored before you can enjoy them. That's crazy.
And the teachers unions are fighting to preserve it.