The reason for this is that the turnover rate for teachers is phenomenally high. Teaching is an extremely difficult and emotionally draining job (especially at schools in underserved districts.) Teachers need a strong incentive for sticking with it, especially when they can get a higher paying private sector job in which they really are done at 5, and really do get the weekend off. So some sort of incentive for longevity is absolutely necessary.
>1. Teacher's wages are negotiated based on education and longevity. Want a $8000 a year raise? Go to school for a couple of summers and get a master's degree. It doesn't even have to be related to what you are teaching. And after you've been there for 30 years getting longevity raises, your pay is 2-3x that of a fresh college grad for the same job. The idiots running the schools think the answer is to give the 30 year teacher a huge bonus and put him on full pension at 52 years of age to replace him with the cheap 22 year old.