By eight year olds.
The children were given a cicada shell each. They made an observational drawing using a 4B pencil and a magnifying glass. They were encouraged to include at least four tones and every detail they observed. "It's not what you think, it's what you see." Good subjects for observational drawing are things that are predominately mono toned, so the colour doesn't get in the way of seeing tones. Eg, shells, dried leaves, seed pods, keys, bones.