It can be hard to get students to understand how to construct a mathematical argument. Proving Prime is a hands-on center activity that has students creating models to support why a number is prime. If they can only make one equal group, they have a prime number. Proving Prime is a leveled activity with number cards that increase in difficulty. This activity works on Common Core State Standard 4.OA.4 Find all factor pairs for a whole number in the range 1–100. Recognize that a whole number is a multiple of each of its factors. Determine whether a given whole number in the range 1–100 is a multiple of a given one-‐digit number. Determine whether a given whole number in the range 1–100 is prime or composite.