In despite to have the same teacher for several years could be beneficial for the students, because they know each other and this could create a wonderful clasroom climate, it seems to me that the students could be beneficial more from having new teachers each year owing to the next reasons;
First of all, I must say that to have the same teacher for several years to what it may seem could be harmful for the students due to the fact that the people have ideas, feelings, expectation...and sometimes we can have bad feelings towars someone.
For instance, if a child has a bad deed with the teacher or some classmate, could happen that the teacher had a bad concepto about this child, therefore, if this teacher is with this child for some years, the attitude of the teacher towards the child could be not good.
Secondly, I suggest that is more beneficial for the students know others teachers not only to know more people, but also for be able to adapt to other people.
All of us, throughout life , we will know a lot of people, thus, we must being able to have relationship whit all of them.
Finally, if I had choose to have the seame teacher or to have a new teacher each year, I would not know what to decide.
I think that both are advantages and disadvantages and depending on the child ,could be more beneficial one option or another one.