It's not really fair for this to be your son's first experience with school. I would be afraid that the constant changing of staff would cause the children to withdraw from the teachers, unable to form that bond that they need, and perhaps even being detrimental to future years in school.
My son loves his teachers, and loves his school, but he was one of those that had to be peeled off of my leg at first. Their stability has made him into a different child...he actually told me 'mommy you don't have to walk me in anymore, I can do it' (yeah right)...but it shows my point. I would hate to walk into my job and find a different boss everyday...it's impossible to think a child would be unaffected by that much change.
Some kids cannot tolerate change, it's just the way they are wired. It would take a LOT to make me change schools, but that may be what you have to do....can you at least change classrooms, so their is some familiarity still?
That's tough, but if you're seeing the effects of it in your son, it's time to act. Remember though, your son will pick up your feelings about his school. If you are having so much trouble trusting them already, maybe you need to look at all sides of the issue and fix it once and for all.