I'm a big fan of collaborative art-making as well as the visual of lots of little things making a big thing. So here are 3 ways I've incorporated those ideas in projects my students have made recently.
My first graders learned about texture and the parts of a tree. They traced their hand and arm to make a branch, filled it with bark texture by using line variety. Then they did leaf rubbings to use the texture of a leaf to make a rubbing-print. The leaves were cut into an organic shape and added to their "tree branch". Once all 4 classes were complete, I combined all their branches into a huge tree overarching the doorway. I wish I could paint on the ground and add the root system too! All their little pieces added up to an impressive display (note to self- don't use poster putty on the glass in the winter- too cold and it doesn't work!!- this all fell down because of a big temperature drop the day after I put it up, but scotch tape to the rescue).The 3rd graders' pattern fish we made a while ago were arranged down the stairwell into what looks like a big fish chasing a little fish. One of the 3rd grade teachers said, "Great! We're just talking about predator and prey in science!" While this wasn't specifically a collaborative project, having a creative way to display the work transforms it into something even more interesting.
The art club finished their "Dale Chihuly" inspired "chandelier" by combining all the tissue-paper papier-mached "snakes" into one splayed mass. I hung it in the stairwell, and have heard all kinds of comments. Usually it's, "WHAT is THAT?!" The only trouble with this kind of collaborative work is that the individual pieces can't be redistributed back to the students to take home.
I think collaboration is a vital part of learning about art. Students feel more connected as a class because they are working toward a greater goal. Every person's contribution is valuable. Contemporary artists often work in a collaborative mode, and therefore students get to experience working methods of artists today in an authentic way. As a teaching artist, I also feel that my own artistic voice is expressed with that of the children, which is very fulfilling.