My DD10 is in OOD at a spec Ed school because of severe LD issues. As a third grader they placed her in an 8th grade LA class. She found it moved "painfully slow" and part of the explanation was that they carefully edited the content for just the reasons you articulate. Much of the spec Ed population would have had difficulty with the content of the readings let alone the types of assignments you are describing. (Folks were concerned about DD - then 8 - but she takes it all in stride. While sensitive in real life she is able to handle just about anything that comes her way in written form...) While it is a spec Ed school they do conform (all too much IMHO...) to common core. This tells me that your DS's content can be adjusted if needed.
I would not wait weeks for an IEP meeting or allow him to continue to have melt downs over this at home or at school. I would speak immediately to the school psych/SW/spec Ed teacher. Their hands probably feel less tied than the classroom teacher's. If this is triggering his anxiety disorder it needs to be addressed. Now. In my experience undoing the damage is much harder than making the needed change when the problem is first identified,
Sadly is this world of ours I am sure yours is not the only child who is triggered by something in the school curriculum. There HAS to be a way around it. Hopefully an experienced person inside the school will be able to suggest an appropriate solution. I would call this morning and get that ball rolling,
Good luck!
