Orchestra is not a core academic course, and will likely be seen by the administration as enrichment, so you will likely find you have less of a receptive audience to asking for an acceleration. If this middle school is like ours, then the grade-level music is a function of the all mighty schedule. Depending on your kids' needs, this wouldn't be where I'd spend my "advocacy capital." (I spend mine on math/science/disabilities, so music is great, but won't be the hill I die on, especially since they do have access to it, albeit not perfect)
Here, the way that a lot of students solve the music pace/level problem is to take up another instrument. Might your kids be interested in learning something new? I know a kid who takes up a different instrument every semester in band. She's still bored, but she's learning.
