As you are meeting your new children the first couple of weeks of school, you can use this interactive activity to “see what they know.” It is fun, engaging and a quick way to assess their number sense. You will begin to see their thought processes as they describe to their classmates the strategies they used to determine the missing number. A hundreds chart can be used for those students struggling to find the missing number independently. Encourage the other students to prove if they are correct by locating the number sequence on a hundreds chart. This activity will provide you with a reference of where to go from here with the standard 1.NBT.1 and move your students into using mental math to determine a missing number.