Teacher and Administrator Longevity

I had the opportunity of going to an Advanced Placement workshop this summer at a high-performing high school up in Cobb County. As I was on that schools’ website, I was looking at some of the teacher and administrative profiles and I noticed that many of the teachers and the administrators have been at that school for several decades. In the district in which I work, you don't normally see teachers or administrators at the same school for several decades. What you often see is teachers and administrators moving from school to school and even from district to district. I started to ask myself well why would one stay at a school for 20-30 years. I then started to put things together and I looked up the schools report card and found that this is a school that has a CCRPI score of over 100. In talking to some of my teacher friends in other school districts and at schools with CCRPI scores that are not that high, it seems that teachers are under a lot of pressure and stress and order to increase test scores. They are also marked down on evaluations quite frequently for simple infractions. All of that plays a role in how long a teacher stays at a particular school. It also plays a large role in administrative turn over. I saw on the news not that long ago where the superintendent in DeKalb County removed several principals because of lack of growth or lack of improvement with CCRPI scores. Now I don't claim to have all of the answers but I know it takes time in education in order to see gains. I guess I'm just wondering about the teaching conditions in high-performing schools versus the teaching conditions in relatively low performing schools. And should this teacher evaluation system be a punitive system? What I feel like is happening is that if you're a teacher in a high-performing school, then the teacher evaluation system just becomes something else that administrators have to do. When you're a teacher in a low-performing school, I feel like administrators are too critical of their teachers and it becomes some sort of a punitive system. I'm not so sure that the teacher evaluation system that we have currently is an effective model. How best can we evaluate teachers without assigning a number to a practice?