This is a great simple activity that lets you walk around and assess who has the concept of addition with single and double digits, without regrouping. When reviewing our math and getting ready to solve a few quick problems, I pair students into groups of two. Each group is given 2 post it notes. I write 5 math problens on the board and we go over the rule that says the bigger number goes in your head and you use your fingers to show the smaller number, count on, and get the answer. They have to write on their stickies: 1. all the numbers that should go in their head (one partner puts the sticky on his forehead) and 2. all the numbers that they will put up their fingers to show (the other partner puts the sticky on her hand). I time this and give them 3 minutes. Then I walk around the classroom to see who has gotten them right. After assessing, students copy the problems into their notebooks and are given 6 minutes to solve them. All answers are reviewed with the entire class. Students who have all correct are given stickers.