Hi Rebecca,
I've taught general music for 34 years and have quite a bit of experience teaching students on the autism spectrum. A couple things come to mind...
1) I wonder if having both parents "helping" might be more help than is necessary... could they alternate? I know when I am learning something new, having two people trying to help me at the same time is often more sensory input than I need or want, and I don't even have sensory processing issues.
2) Many students are successful in my music classroom because there is a regular routine for them to follow. I provide a schedule for those who benefit from such a thing so that they know what to expect as the time passes during their music class. You could do something similar for this ringer if your rehearsals follow a regular kind of routine, perhaps something like:
-Body stretches
-Bell warm-up
-Piece #1 (name of whatever you are going to work on first, even with specific measure numbers if applicable)
-Piece #2
-Polish bells
-Put bells away
Obviously, I don't know exactly what your rehearsal routine is, but you get the idea. For some classes, I post the schedule for the whole class to see. For others, I have the schedule on a clipboard and the student just moves the schedule card over once the activity has been completed (see example below). Schedules can be like security blankets for students with anxiety.
3. If there are particular cues that you will need to give the ringer, picture cues might be even more effective than verbal ones, especially as it can cut down on the helper repeating everything you say. I've included an example I use for when my students are playing the Orff instruments. In this case, having a helper (peer or adult) show this to a student who is playing too loudly is way more effective than having the helper keep telling the student, "Play softer please." I can imagine that picture cues might be helpful in a bell rehearsal as well. There are computer programs that help with these types of things, but honestly, I prefer to take pictures of peers and make the cue cards myself.
I had a third grade class today with a student who has autism, and although his verbal communication is limited and his autism might be described as severe, if you came in to observe and I didn't point him out to you, you wouldn't have been able to pick him out from his peers... and today's activities included playing a rhythm game involving syncopation, learning a pentatonic melody on the Orff instruments using solfege, and then playing it in canon... all of which he did flawlessly. I have another student, a fifth grader, who I've taught for years. He was new to me as a first grader, and I got an email from his mother the first week of school that year letting me know that he really disliked music and was sensitive to the sound of the triangle. Five years later, I can report that he's been entirely successful in my class... a shining star, in fact. (I've never used a triangle with any class he's been in... and it's a sacrifice, lol, that I've been perfectly willing to make.) I applaud you for doing what you can to make your bell rehearsals successful for your new ringer. Regardless of whether this child continues ringing for years to come, you will be a better director for the problem solving that you are doing and the creative thinking that you are employing... good for you!
Cynthia Sepuits