Reply To: Dealing with ability gaps
While I will admit that I am a student, not a teacher(yet, working on my college degree now), there might be a few things you could try.
First, are private lessons an option to help the kids catch up? Or, if you can’t do all 12 individually, can you schedule maybe an hour a week to work with just them, and help give them the catch-up they need?
You might want to also consider a buddy system. Meaning, place your inexperienced players on the same part as your experienced players, and have your experienced players show them fingerings, tonguing, etc. along the way. This will (1. give them a secure idea of what their part is supposed to sound like, (2. give them the quick helps that they need while you are in class, and (3. give them a source of encouragement when they feel like they are having too much trouble.
The only other thing I could suggest is varying your levels of music that you play. You might want to consider adding 1-2 easier pieces in addition to your pieces that stretch your students’ abilities. This will give your beginners something that is in reach, and it will a chance for you to work your more experienced players on some of the finer things(phrase shaping, articulations, watching the conductor etc.) that would usually have to wait on due to note learning. If it comes down to it, if you think some of your pieces are still too hard for some of your newbies, you can either take them off that piece, or move them to mallet percussion, or a different instrument part that is easier within the piece.
I hope this helps! These ideas are some of the solution my own MS/HS director has done of over the years, and it’s worked fairly well. Good luck!