Check out this awesome packet that includes 10 different worksheets with correlating answer keys. This mental math coaching exercise covers the topics of addition and subtraction and each sheet includes six problems. It is meant to be played one student vs one student in which student 1 coaches student 2 to find the sum. The sixth question on each one has the sum but is missing a box and students need to figure out what is missing. This is a great student-centered activity in which students support, explain, and teach each other while building number fluency, place value understanding and mnetal math skills. Directions are included!