Reflection: Modeling Transforming to Compute Larger Numbers - Section 3: Student Practice


During student practice time, I realized two areas that students needed further support at two different points in the lesson. For each of these moments, I asked students to stop what they were doing and join me on the carpet in ten seconds (I counted down from 10 and celebrated punctual students). I am a believer that on-the spot modeling is an important element of student practice time.

For the first 2-minute gathering, we discussed a context in which we would adjust one number and then adjust the other. I wrote 39 + 56 on the board and explained: Let's say that Sarah came to my house and cleaned one day and I paid her $39. A week later, she came back to clean again. This time, my house was a bit messier so I paid her $56. Many students were astonished at how much I was willing to pay Sarah! I continued: On day one, I gave Sarah $40 and said, "We'll just adjust your pay next time to make up for the extra dollar." Would I take $1 away from the $56 or add in another dollar? Students immediately responded, "Sarah needs to give you a dollar back because you paid her too much." They got it! 

At another point, I noticed students were inefficiently subtracting and adding. For example, If a student had 6828 - 3491, many students were subtracting one from both numbers to obtain 6827-3490. I pulled students up to the front carpet once more to model how to change the problem to 6837 - 3500. Either way, students will get the same solution, but the second problem will be easier to solve using mental math. Immediately following this 2-minute gathering, I celebrated any students implemented this strategy. 

  Modeling: Reflection
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Transforming to Compute Larger Numbers

Unit 5: Adding & Subtracting Large Numbers
Lesson 14 of 16

Objective: SWBAT use transformation to check the addition and subtraction algorithms for accuracy.

Big Idea: Students will adjust both addends or both the subtrahend and minuend to make computation easier.

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