Nurnberger-Haag, Julie, and Jamie L. Wernet. “Sparking Surprise: A Negative Number Game to Promote Productive Concepts of Addition and Subtraction”. Ohio Journal of School Mathematics 82, no. 1 (June 29, 2019). Accessed May 5, 2024. https://ohiomathjournal.org/index.php/OJSM/article/view/6663.