I can't say that people "yell" at DD but they have pointed out her disabilities as a criticism. I respond immediately and strongly. I don't know about your DS but my DD is very, very sensitive so something like this stays with her for a very long time. Just the other day I spent a half hour on the phone with the SW drawing the line from actions and statements last fall that I believe have led to DD's increased anxiety and insistence on being sent home this week.
I had to push hard when they were inconsistent about providing para support and the teacher was disregarding the IEP requirements for support. Once they finally started to provide a substitute she refused to write for DD (not sure just what she thought she was there for...) and called DD - and I kid you not - "lazy" and "disrespectful" for "trying to get out of doing her own school work." DD started crying and refused to work with her anymore. To the school's credit they made this substitute para apologize to DD but they allowed her to continue working with her for the rest of the day. When she asked for an anxiety break they sent her to take a walk with this woman - the one who triggered the anxiety to begin with. I am not sure but I think during the time alone with DD this woman laid a guilt trip on her because ever since she has been very nervous about getting any of the paras in trouble and won't report anything improper.
At our parent teacher conference last fall the first thing the classroom teacher did was complain that DD "is very slow putting her things away in the morning." I said "You do realize DD is dyspraxic - right? She does everything slowly..." The teacher backed off the comment but it gave me great insight into what is likely going on. We have noticed a pattern that many if not most mornings DD develops some sort of physical complaint during the first minutes of the school day. In my conversation with the SW the other day I pointed out that if the teacher understands the situation so little that she can comment on how slow DD is to put her things away I have to assume that there is something happening at that time that is triggering DD's anxiety. Of course they do not admit to anything happening and this is a school that prohibits any sort of parental involvement. In other words there is no one other than school personnel to rely on for an accurate report of the situation.
Obviously your school does not like this accommodation. It is likely expensive and clumsy to administer. You have also shown yourself to be a parent that will hold their feet to the fire. Too bad. Their annoyance or your willingness to be a hard a** does not get them out of their obligation to meet your son's needs. I would be all over the woman with a megaphone like white on rice. I think you need to have very precise info on what the para is comparing between your ds and Peter. Maybe she was referring to his pencil grip or some other specific thing your ds is supposed to be working on. If it's just that Peter is doing his own writing and your ds is not that is definitely a problem. I'm not really sure how you find that out though...