*“Sam Vandervelde’s Criss-Cross” is free on this website for one week only. It’s an excerpt from 312 Things To Do with a Math Journal, available as an ebook at my bookstore (Thank you for cutting out the middleman!) and in ebook or paperback through many online retailers. Read more about my playful math books here.*

Many parents remember struggling to learn math. We hope to provide a better experience for our children.

And one of the best ways for children to enjoy learning is through hands-on play.

This game offers students a chance to practice mathematical reasoning (and possibly notice a connection to the Euler characteristic).

## Sam Vandervelde’s Criss-Cross

**Math Concepts:** topology, strategy.

**Players:** only two.

**Equipment:** pencils and blank paper.

### How to Play

Draw 3–8 dots spaced out like the corners of a large polygon. Add up to 7 more dots inside the polygon.

On your turn, draw a line (or curve or squiggle) between two currently unconnected dots. If two dots are already connected, you may not draw another line between them. Lines may not cross. The player who can’t move loses.

For more information on the game, including teacher’s notes and discussion questions, see the Math Teachers’ Circle website.

### In Your Math Journal

Use the game as a journaling prompt. Here are some sample questions:

- What is your strategy for winning?

- Do you think this is a fair game, or does one player have an advantage?

- How would you count score, so you could compare your performance from one game to the next?

- How would you modify the game rules? Is your version easier or harder than the original game?

- Do you prefer logical strategy games or games of chance? Or do the best games have a bit of both? Explain.