Escher style Geometry Art from J. R. Masterman's 9th grade geometry class

whale symmetry art, a first-time tessellation attempt by a 9th grade child

WHALES by Ornella

Here's a beautiful piece of symmetry art. The curling line in the water is a particularly nice bit of stylishness.

This is not the ideal example of an Escher-style tessellation, though. Can you see why? It's the air and water. Water and air have no form, and we can call them "background", so they're a kind of gap. Tessellations should be made of foreground shapes that repeat to fill a space without gaps or overlaps.
gap in a beginner's tessellation
Now, here's something tricky to explain: If it were not a picture of animals and air and water, then this would be a fine example of abstract-style tessellation. Why? Because we wouldn't interpret those "water" areas as water, so we wouldn't think of them as gaps where the foreground things let the background show through. Instead, we'd think of all the parts as repeating solid foreground abstract shapes.