3rd grade should be introduced to not only shapes, but how shapes are 3-dimensional forms. I got this idea, again, from my fabulous colleague who did a similar lesson with her Art Club.
We both used a poster of Paul Cezanne's still life paintings with fruit on a table. (Something similar to this painting).
Every student was provided with a colored rectangle for each fruit and a brown piece for the bowl. We started by drawing out fruit shapes, cutting and pasting them. I showed them a trick with the grapes, to cut a slit up the center, and have it dangle down the front of the bowl.
On Week 2 of the project, one of the teachers had some 3-D foam shapes handy. I turned the lights off, and used my flashlight App on my i-Phone (haha!) to ask them questions about what they see. We examined that all forms will have both shadows and highlights with a given light source, no mater where that light source may be. We then sat down and did a shape/form/value study on paper, to use as a guideline for our collages.
I am pleased to see such a variety of "strokes" - each student uses the utensil differently, different pressures, different directions, scarcely using the pastels or heavily using them - either way the students definitely got the concept!