[Image found in here.]
There’s nothing wrong with that student’s sketch, because it has little to do with artwork. Duplicating individual squares of a grid is a geometric exercise in hand-eye coordination and nothing more.
On the other hand, the sketch is awesome. Ignore the grid and mock the assignment. Realism is what cameras are for.
The key to drawing is to sketch what you see, not what you think you see. Forget what it is you’re trying to draw, squint your eyes and sketch out the dark spots, then add the medium spots. The white spots will figure it out on their own.
Look at a tree. It’s not a flat lollipop, and when you draw it, make sure there are holes in it for the birds to fly through.
Grampa Strutts gave me that advice a long time ago. Then he showed me this book. Download a copy before it’s gone and study it. It’s Beyond the Valley of Awesome.
[Related post here.]