Use and explain the totals below method using words, math drawings, and numbers

In this lesson, students use previous knowledge of place value and expanded form to solve addition problems. They decompose two- and three-digit numbers, add like-units, and record the totals horizontally. Then students transition into the vertical form of the method when they decompose the numbers mentally, add like-units, and record the totals. The "totals below" written method give students the option of adding from left to right or from right to left. Students explain how each step of their math drawings relates to this written method.