This lesson is intended to be covered over a two-day period with a group of second or third grade students. It could also be used with students who are having difficulty mastering the traditional algorithm for adding larger numbers without and with regrouping. The first part of the lesson covers the adding left to right mental math strategy. The second part of the lesson covers the break apart or decomposing mental math strategy. There is an accompanying worksheet that matches exactly this presentation. It is a separate purchase. This lesson can be used in one classroom only and may not be shared without purchasing additional licenses. Please purchase the separate worksheet that matches this presentation exactly. This helps students follow along as you move through the presentation. This lesson is based on the math standards for the state of Washington for second and third grade.