Should elementary children have one main teacher or several?

I'm wanting research oriented answers based on the developmental stages of upper elementary children - 4th and 5th graders. We are going from two teachers -one teaching math/science and the other teaching language arts/social studies - to 4 main teachers: math, science, language arts, social studies. These children will also see a PE teacher and a fine arts teacher. The reason given is that the teacher can specialize instruction and thus better instruct the cles - raising test scores in the process. My thought is this is too much change for this age child and the primary benefit is to the teacher who decreases preparation time. Any research? Studies? Personal experience? I know that the answer will change with the intellect and personality of each child - but ... in general?