I have a somewhat simplistic but seemingly effective way to solve many these issues. I suggest that much time can be saved if the teacher is assigned a class of students and rather than moving the students to another teacher each year, move them all together. The time a teacher is paid while the students are on "summer break" can be utilized for the "continuing education" teachers are required to participate in so that they may be prepared to move to the next level. No teacher will acquire "tenure" until they have graduated a class of students. This will be a non starter for the unions without question however. I realize this only solve SOME of the issues, others must be addressed much differently, legislatively.
Your plan is novel and has some merit. But, it's like asking an engineer to quit focusing on building the landing gear an instead build the whole airplane.
- Teachers right now customize their classrooms, curriculum, instruction style, classroom management, etc. around working with students at a particular stage in development.
- It takes more than a summer to prepare and new grade level and excel in teaching it. There's a big difference in knowing the subject matter and being able to teach it effectively.
- Many teachers in upper grades specialize in one subject and, in effect, become experts. There's no way a French teacher should teach chemistry.
- Giving students different teachers as they grow can cut both ways. There's a period where the new student and teacher much form a working relationship and time is lost there. But, giving student the opportunity to interact with many adults actually strengthens them by allowing them the opportunity to experience many different relationships and interactions.