Great way for students to practice finding missing addends with sums up to 20. They'll enjoy the Christmas theme while practicing a much needed skill. There are two sets, for differentiation purposes. Set A has lower sums. Set B has higher sums, but only up to 20. Use Set A first. Once your students are ready for a bit more challenging missing addends, introduce them to Set B alone, or combine both sets for a much longer activity. There is a recording sheet for each set.