This kind of thing happens all the time- both last minute schedule changes and
pre-arranged schedule changes- field trips, assemblies, career day, early
release, testing days, etc. On both my elementary campuses, special area
teachers are expected to accommodate changes that keep students from missing
specials time, but not expected to go ahead and make up class times if students
I don't think it's handled quite the way you put it- teachers are not permitted
to rearrange the schedule and them impose those changes on the special area
teachers. (principals do that, but teachers don't) What usually happens is
the teachers discuss it with us and we work something out. Most teachers will
go all out to avoid missing specials and would not willingly schedule a field
trip during their own planning period.
Now, this stuff goes both ways on my main campus. We special area teachers
schedule things that effect the classroom teachers schedules and they
accommodate us- program rehearsals, trips to the museum, special performances.
Just last week I took the 4th graders (with their teachers) to a photography
exhibit during their special area/ planning time, and the teachers didn't get
to make that up (and didn't ask) Some of the other grade level teachers
wouldn't have gone for that.
Usually changes happens in a friendly way without stressing people out too
much- but sometimes it gets to be a problem when communication breaks down!