**Math concepts:** Addition, Classification

**Equipment: **Domino Set

**Recommended Grades:** K, 1, 2, 3

**Time:**15 – 45 minutes

**Common Core:**K.OA.A.2, 1.OA.B.3, 1.OA.C.5, 1.OA.C.6, 2.OA.B.2, MP1, MP6, MP7

#### Overview

What is the middle domino? This question launches the project of sorting the dominoes

from least to greatest.

#### Why We Love Domino Sorting

Domino sorting is a perfect math challenge for a station or small group activity. This

activity combines addition and sorting in a completely natural way.

#### The Launch

- If students have never explored dominoes before, let them play with a set for ten minutes before launching Domino Sorting.
- Once students have had a chance to play, pose the question: which domino is the exact middle domino?
- Let students chime in with ideas—these ideas will inevitably be various and difficult to defend. Make the point that to find the middle domino, they’ll have to put the set in order from smallest to biggest. But which domino goes where?
- Students may suggest this natural answer: whichever domino has the most dots on it is the biggest. For example, the (4,5) and (3,6) dominoes on the right both have the same number of dots (9), so they go in the same pile.
- The goal from here is simple: each group of kids gets a full set of dominoes. Their goal is to sort them into piles based on the total number of dots on each domino. Once they do this, can they decide which domino is the “middle” domino?
- Once students can sort dominoes up to 6 by 6, you can pose the question for the larger set of dominoes, which goes up to 9 by 9.

#### The Wrap Up

You can close this activity with a class discussion, or by having each group write down

which domino they think is the middle domino, and why.

**Tips for the Classroom**

- There’s always a danger when you bring dominoes in to the classroom. You can use paper cutouts, or be very clear about appropriate use.
- The final arrangement of dominoes has a beautiful symmetry. Drawing students attention to the visual symmetry is a good idea if they don’t notice it on their own. Notice, however, that the “middle” domino still isn’t clearly defined. It could arguably be any of the ones that have six dots on them.

## About this Lesson

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