Activity Type:

Problem Solver +/- (Adding/Subtracting)

Quick Description:

In this modification of tic-tac-toe, two players take turns writing numbers 110 in a 3x3 grid, trying to create a horizontal, vertical, or diagonal line of three numbers that sum to 20. (Adapted from Kamii & Housman, 2017.)  

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Special Thanks To

Institute of Education Sciences
The research reported here was supported by the Institute of Education Sciences, U.S. Department of Education, through grant numbers R305K050157, R305A120813, R305A110188, and R305A150243. to the University of Denver. The opinions expressed are those of the authors and do not represent views of the Institute or the U.S. Department of Education.