Here's a cool Valentine's project that teachers shading skills. I've taught this to Grade 6 students the past few years and they really enjoy it.
I pre-cut manila tagboard into small squares. Students folded them in half and drew half a heart and they cut it out as well as the center. The hearts should be at least 1 cm thick so they're not too fragile.
Then they trace it onto 9 x 12" drawing paper. They slightly overlap the hearts and then erase the correct lines so the two hearts are interlocked. This takes a bit of practice.
Keep tracing and overlapping the hearts until the page is filled nicely.
The next class I showed students how to shade the hearts so they look 3D. They could shade using either pencils or coloured pencils.
Some Grade 6 results: