This is actually a project I did in high school. I still have my original believe it or not.
It's quite an easy project: good for practicing value and shading.
This is a technique used quite alot in advertising and design: scale exaggeration. You could also discuss the design principles; this one relating to Proportion and how artists can manipulate and exaggerate proportion to express moods and experiences.
Here are the directions: Find an appropriate image in a magazine: you're going to cut off part of the image and visually 'stretch' the missing part using pencil. Using figures tends to be quite popular but it can be anything, really. If students can only find colour images, then just photocopy them so they have a black and white image to work with. Glue the magazine image onto a piece of drawing paper with a glue stick and then you're ready to go. The key is to make them match the photo in terms of accurate shading. You want to fool the eye.
These are Grade 9/10 examples