In these cases I have close communication with the family, looking for what goals they have for the student being in band. I follow their IEP/504 and I work with any case manager in the school. Depending on the student, sometimes they are their to be social with other students, I give drum sticks and a drum pad and help them find beats. They do not go to contest with us, but are there for all concerts and campus performances. Others are a little engage and were able to start learning clarinet.
Again, this is a case by case situation that you must communicate with all other parties involved.