In my certification program (which had nothing at all to do with music) one thing that all of my professors stressed was the need for careful consideration of differentiated instruction. Students have different needs and abilities and instruction should be adjusted accordingly. For example, one student might need extra time to complete a reading passage or a test, or might get a simplified reading passage, or fewer questions. In orchestra, it's hard for us to differentiate in these ways because most of what we do happens in real time group performance. I can't give Joe 30 extra minutes to play the second violin part (although I could--and have--create simplified parts).
In my junior high orchestra, I have 30 students across three grades: seventh, eighth, and ninth. I have four different instruments in my orchestra: violin, viola, cello, and bass.
Some of my students have been playing for five years. Some have been playing for three weeks. A very few take private lessons and have the luxury of practice time and space (I usually give my groups seven minutes at the beginning of class to tune, warm-up, and practice, assuming that most of them don’t often play at home. This also gives me time to take attendance, fix instruments, or do other administrative things).
Some are strong note readers but weak instrumentalists; others are weak note readers and strong instrumentalists. A few are strong note readers and strong instrumentalists, and some are weak readers and weak instrumentalists.
Some students have IEPs and/or 504 plans that indicate they need to be seated near the door, or close to the instructor. I have to at least try to accommodate all of these different needs, but the context of a large ensemble class makes that really difficult.
Do I develop 30 different worksheets? Some in treble, some in alto, and some in bass clef (for both cello and bass)? Some with just open strings, some with notes in first position, and some with third position notes?
If my cello section is on the opposite side of the room from the door, but I have a cellist who needs to have easy access to the door, do I rearrange my orchestra? Have my one cellist sit among the first violins? If the person who earned the lowest score on their playing test (and thus is sitting last chair) is the person who needs to sit closer to the teacher, how do I reconcile those two things? I know that I have to make my best effort to honor these circumstances, and I do. I have more experienced students sharing stands with less experienced ones. Seating in my orchestra is not a meritocracy--I carefully consider who's sitting where.
And yes, yesterday I handed out about twelve different worksheets that were tailored to the needs of my students as best as I could without completely losing my mind and spending 90 hours on them (I do my best to work within contract hours). I guess my point is that we music teachers/ensemble directors need to differentiate too but we have a whole different set of circumstances to consider.