I love this lesson, students love this lesson and they all turn out so very awesome!
I did this lesson last year using all oil pastels and although they turned out just as wonderfully it took us 4-5 classes to finish compared to this year only taking 2-3 classes to finish.
Instead of having students create their sphere using oil pastel we painted. On the first day of the lesson we talked about form and value and how you make something on a 2D surface look 3D. Using a compass students created a circle on a 12x12 paper. I gave students a quick demo and then students chose the color they wanted to paint their sphere. Paint was distributed and we began paint all together. To start I instructed to paint the entire circle using the local color then students added white paint for the highlight and black paint for the shadow. It's very important that students don't use the white after they use the black otherwise all of the colors will start to turn grey.
On day 2 of the lesson using oil pastels students chose a sport and adding details to the sphere using oil pastels. They also used oil pastel to add something in background, it did not matter what it was as long as the background was filled. About half of the students finish on the 2nd day of the lesson and most students only need about 15-20 minutes to finish on the 3rd day.