Double-Digit Subtraction - We Can Do It

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Objective

SWBAT use manipulatives and drawings to solve double-digit subtraction problems.

Big Idea

It takes practice to complete double-digit subtraction problems so today's lesson allows for that practice in several subtraction centers.

Warm Up

10 minutes

I begin today with a subtraction facts practice page. The page has 25 problems up to 20 - 10 (all subtraction) to complete as quickly as possible. I create the page at MathFactCafe.com where I can put in the parameters for my subtraction page. I give students 2 minutes to complete as many of the problems as we can and then we correct the problems together so that students get immediate feedback regarding their fluency. 

Subtraction Centers

50 minutes

Today students will visit several subtraction centers. At each center they will be able to practice subtraction. I start by explaining each center to the students. I have a series of problems for Centers 2 and 3 for children to use when building the numbers. The problems are on large sheets and posted for all students to see. Each center encourages students to makes sense of the problems and persevere in solving them (MP1).

Center 1: Subtraction fact practice on the iPad. Students have the option of using several subtraction fact practice programs on the iPad to increase their fluency with subtraction facts. They use Math Bingo, Flash Card Math, and other programs that allow for immediate feedback and let students know if they are correct or incorrect. 

Center 2: Ten Frames Subtraction: Students start by building the larger number with filled-in tens frames for the ten's digit and blank frames that they fill themselves with chips for the ones. Now they decide if they can subtract the necessary ones by taking away chips. If they can not, they turn one of the filled frames into a frame of chips (regroup) so that they now have enough ones.

Center 3: Subtraction Using Place Value Houses. Students build the larger number in the upstairs of the house and the number they are subtracting in the downstairs of the house. They subtract by matching the minuend blocks with the subtrahend blocks and removing them from the house.  They regroup when necessary to match tens with tens and ones with ones. 

Center 4: Paper and Pencil Double-Digit Subtraction: Students may draw the base 10 blocks or tens frames to solve these regrouping problems. Students need to choose the tools that are appropriate for solving the problem(MP5).

Once I have explained all the centers, I break students into groups, based on understanding of double-digit subtraction. I want homogeneous groupings so that students who are more confident can begin with the paper and pencil subtraction center. I get each group centered for each round of centers and then I work mostly with the group visiting Center 3. This is the center that takes the most support for students to do. 

Ongoing Assessment

10 minutes

I ask students to return to their seats. I give students 2 double-digit subtraction problems to complete. One of the problems requires regrouping and the other does not. The problems are 71 - 46 =, and 65 - 32 = .  I tell them they may use any of the strategies that they have used today, or previously, to solve the problems (MP1).

I collect these problems to assess student progress with double-digit subtraction.