BK1 nicely said. That age thing is a huge factor. Both teachers and administrators are terrified to move children up because of the age difference. They are afraid of the social and emotional implications that could arise from these different ages interacting together.
When my ds went to public school their where Kindergartners and 2nd graders on the play ground at the same time. I was visiting with my son that day and he wanted to play with the 2nd graders. The Vice principal came over and told my son that he was to young to play with the 2nd graders even through they had already accepted him and he was having a blast. He then started playing by himself b/c he couldn't relate to the other K's.
When teachers and adults start telling children not to associate with kids younger or older then themselves that is what leads children not wanting to socialize with kids beside their ages and when they have to they don't know how and this is what causes the problems that teachers and administrators are afraid of. But if it was the norm for a 5 year old to be with 8 year olds then there wouldn't be any problems.
