I think a most important part when faced with an unruly class is to
acknowledge the good behavior. After getting the attention of an unruly
class I usually use my quiet voice to apologize to those who have tried to
behave as expected. I list the good behaviors they have modeled and thank
them for it, with eye contact. This usually gets the attention of those
borderline kids who have been sucked into poor behavior, and the chronic
behavior issue kids become lonely with their choices.
I did take a 3rd grade class back to their homeroom once, but I had them go
to their desks and put their heads down. The homeroom teacher was using the
room for her planning period, which is a reasonable expectation for her. The
students had to remain quiet, so she could continue her work.
If I assigned a writing project, I'd make sure it was related to art in some
way. I'd probably point out that their behavior indicates that they choose a
writing project because they have shown they can't handle a hands-on art
Another approach I've used is similar to San D's. First, take a run around
the playground, then return to the room and brainstorm a minute or two about
ideas from the event that caused the disruptive behavior (just coming in
from a test). Then pass out simple materials such as pencil or crayons and
paper to illustrate their feelings and thoughts about the event. If they
claim to have no feelings about the event, then ask them to draw something
they saw while running their lap outside.
Good luck, and remember, we have all had days like the one you've described.
They help make the good days seem simply glorious.