Thank you for your interest in NCTM’s Illuminations. Beginning in mid-April, all Illuminations content will be moving to Interactives will remain openly available and NCTM members will have access to all Illuminations lessons with new filtering and search options. We hope you will continue to utilize and enjoy these resources on

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Pre-K-2, 3-5
Number and OperationsGeometry
Math Content:
Number and Operations, Geometry

By yourself or against a friend, match whole numbers, shapes, fractions, or multiplication facts to equivalent representations. Practice with the clear panes or step up the challenge with the windows closed. How many socks can you win?

This interactive is optimized for your desktop and tablet. 


  • Level:
    • numbers 1-6
    • numbers 1-10
    • geometric shapes
    • multiplication facts
    • fractions
    • fractions, decimals, and percents
  • Players: one or two players
  • Games: hidden (covered windows) or revealed (glass windows)

How to Play

  • Within the game, choose any two windows.
  • If the images under the selected windows are equivalent, a match is made.
  • In one-player mode, the game ends when all six matches are made. In two-player mode, points are earned for matches, and the player with the most points wins.
  • Wins will translate into socks, which will hang in between the buildings.

Try creating your own game of concentration use index cards to teach any math topic.

For example, you could show a linear equation and match it up with its graph or table of values.