Introduce the lesson to students by telling them they are solving two- and three-digit math subtraction problems by regrouping. Give each student a piece of paper and a pencil. Have students fold their papers once across, then vertically. When students open their papers, they have four boxes. Next, write four two-digit math problems on the board and four three-digit math problems, all ending in zero. Direct students to copy one problem into each of the boxes, using the front and back of their papers.
Walk around the classroom to check that students copy the problems correctly, with one problem into each box, front and back. Once complete, call their attention to the front of the class. Inform students they will regroup numbers to find the difference for each problem. Inform students that all the problems end in zero, requiring that they apply the process of regrouping to subtract the number below it in the problem, since the top number must be greater than the bottom number.
Solve the first problem as students observe. Say to the students, "since I have a zero at the end of the first number, and the number subtracted from it is more than zero, I need to regroup." From this point on, verbalize for students each thought involved in completing this process, including questions. Thinking aloud models the thought process to correctly apply a specific problem-solving technique. Students see and hear what should happen in their heads when they regroup numbers independently.
Direct students' attention to the second problem written on the board. This problem is completed using student input. Ask for a volunteer to tell you how to solve this math problem through regrouping. As the student tells you how to regroup to subtract the numbers, encourage the student to think out loud as you did in the first problem. Do this by asking questions to the student, which require accurate responses, and explain the process of regrouping. Once this problem is complete, ask for students to solve the third problem with a partner. Allow students enough time to complete this problem before checking as a group.
Have a pair of students volunteer to go to the board and to show their answer on the board. One student writes and the other explains the process. Review the steps the students took as a group to confirm accuracy. Instruct all students to complete the remaining five problems independently. As students do this, gather together the few students who appear to struggle with the process, and work at a table with this group, providing additional modeling of the process.