As they arrived in class, I told them to get their sketch books and to make 4 rectangles on each of three pages, all different shapes and sizes. As they did so, I placed 5" x 8" pieces of card stock on the tables in front of each student and then doled out a variety of objects onto the card stock; mini-still life setups. There was a piggy bank, a jar with dice in it, binder clips, a cream pitcher, some building blocks, a ceramic chicken, jar with brushes in it, a miniature trophy, etc.
I explained to the students that I would roll a die, which would tell how many minutes they would draw, (maximum time allotted was 3 minutes) then we drew a card from a deck. If it was black, they could draw anyway they wanted. If it was red, they needed to crop the drawing. Then.. drum roll, if they pulled a face card, it would be a no eraser round! They gasped.
We had a ball, and they took risks, pushed themselves, and realized that 3 minutes is a long, long time when you are drawing the essence, the essentials of the object in front of you. They cropped their images in very interesting ways, excitement! We had a lot of laughs. I had a large stopwatch running on my smartboard, some music in the background, and they happily rotated after every round.
Everyone left happy, and successful, and feeling pretty accomplished... a good day.