Crossword puzzles are symmetrical?! That’s usually the response I get after students have been given a chance to look through blank crossword puzzles I’ve cut from the paper.

Then I show them how all crosswords are designed with 180-degree rotational symmetry. Starting with 90-degree rotational symmetry, we rotate an object 1/4 the way around the circle. See photo below. Then we rotate an additional 90 degrees so that we end up with a turn of 180-degrees. (We’ve done work in class on angle measurement so students are familiar with degrees in a circle.)

I then pass out 2 copies of a crossword puzzle/team. Holding the two puzzles one on top of the other in the same direction, they hold both puzzles up to the light and slowly rotate one of them 180-degrees. They should see that after the turn, the patterns fit nicely on top of each other. They are usually amazed.

So now it’s time for them to create their own puzzles. I like to use centimeter paper that is 15 x 15.

They begin by coloring in boxes on one side then flipping the paper 180-degrees and counting over and drawing in the exact same boxes. When students use different colored pencils or pens, the result is pretty nice.