From a teacher's perspective, I've taught in a middle school 6-8 that is a separate entity, as well as one that was on the same campus as the elementary and high school and one that was 5-8, (Yes, I move a lot blush ) - I understand what the admin is saying about keeping the 6th graders separate from the 7th and 8th graders, and yes, it is partly so the parents don't freak out, but it is also because the differences between 6th graders and 8th graders is enormous!
This tends to be more visibly noticeable with the girls, since there is a large physical development difference between a 6th grade girl and an 8th grade girl (and yes, it is hormonal - oh boy, is it ever... crazy ).

Most 6th grade girls are still nice to each other, and themselves, however, somewhere between 7th and 8th grade many of them go through the start of puberty and turn into mean, pushy, overbearing girls who will want to be your best friend one minute and then go behind your back the next to stab you in the back because you either looked at a boy they liked, or you got to get the newest fashion they wanted, or simply because they can. Most of the time the girls do this without being able to control themselves - it is their hugely unstable hormones to blame here. But it can be a big shock for a 6th grader to have to deal with girls like this on a large scale. Often times the 8th graders make it a point to bully the 6th graders because they are so young, developmentally that they seem like babies to the "older and more mature 8th graders".

For the boys the differences aren't usually so great, but their slower rate of maturity gets more noticeable as they go through middle school. While most girls are ready to have boyfriends, many boys are still looking for friends to play cards or computer games with. The boys have their issues happen in 9th grade, more often than in middle school.

How this plays out for gifties is dependent on their own personality, just as it is with an ND child. All kids have to go through puberty at sometime and some handle it with more grace than others - I have one niece (PG) who when through with very few dramas and is now finishing her junior year in high school still a happy teen, her sister (M/HG) has had a horrible time going through middle school and now at the end of 9th grade is still having problems with issues related to going through puberty and trying to figure out who she is. The older one saw what other kids were doing and consciously chose to not get involved in it. The younger one saw what was happening and got involved in it to see what it was like (a way to fit in) and is still pretty unhappy about the path she picked.

Sorry for being so long winded. We were discussing a similar issue at work today in relation to 9th graders and their changes within a school year.