The benefits:

I doubt that the lowest possible turnover rate is compatible with the best possible education. Turnover has costs, but it also has benefits: fresh blood, lower burnout rates, and an incentive for teachers to keep performing. The whole idea of hiring someone in their early twenties and employing them forever seems like an unhealthy organizational structure to me–in the military and old-school law firms as well as teaching, though the military and law firms do more to weed out the number along the way. It breeds an organization that is insular–resistant to new ideas, suspicious of outsiders, resentful of its nominal clients. We should be looking for ways to make teaching more open to part-timers and people in second, third, or eighth career cycles, and to make it easier for teachers to move around between schools and districts, and between teaching and other industries.

It will never happen, though, as long as the NEA retains its power, because it’s never about the children with them. And it’s another good argument against public-employee unions.