9 year olds.
The class had been to see a local artist. A previous class I worked with had also been to see him. A tolerant man.
He shared with them not only his current paintings, but also the thesis he wrote on Light and Science! Absolutely perfect! The main themes to come out were that observation is the key to art - looking at light source and shadows created depth and realism.
I had a selection of plastic fruit, which I painted black. I asked them to draw one with an emphasis on where the light source was. They repeated this exercise using black paper and white crayons.
I set up a ball on a tall tube, with a beam of light shining on it. The day was bright and I can't black out the room easily so the shadow on the ball was difficult to see. Anyway, they made a shaded drawing of the ball three times with coloured pencil.
Their background was an optical illusion which took the eye away into the distance. This was made with marker pen and black paint. The three balls were cut out and attached to the optical illusion, with consideration as to the position of their light source.