Each year as an introduction to portraiture using a grid method, I have my Art students enlarge and draw what appears to be a totally non-objective image. I give them a small square with the image on it, and they draw it onto a larger square. This year I gave everyone the same type of mechnical pencil to use to try to keep the shading more consistent than it's been in previous years.
The kids don't know what they're drawing until all of the squares are put together to form a picture!
Intro to this exercise involves doing value scales and also doing some preliminary drawings that simply involve copying various shapes.
They are given 1/2" squares of a Photoshop-altered photograph and enlarge the images onto 2" squares of white paper.
All squares are coded, and when students complete the 2" squares, they glue them onto a large sheet of paper, to form a large, mosaic-like portrait.