Reflection: Developing a Conceptual Understanding Crossing Over 100 - Section 2: Teaching the Lesson


Students had no trouble counting by tens, but trying to switch back to counting by ones for the stepping stones had some children confused. I went around and asked students about the numbers they were using for stepping stones. One of the children wrote 181 on one side of the river and 191 on the other side of the river (around her 180). I asked her which number was one more and she knew that 181 was 1 more than 180. I asked her if 191 was one less. She said yes.. no.. and then shook her head. She erased the 191 and then wrote 171. Again, I asked her if that was one less than 180. I had her count on her number line. Oh its.. and then she paused. It was clear that she was not able to think of one less than a 3 digit number.  I covered the one hundred and said ok lets think. If I had 80 and wanted 1 more I would get to 81, like your 180, 181, but what comes before 80? She said 79 and then said, "OH, 179!" and she smiled.

Connecting to the reasoning she applies to working with 2 digit numbers helped her when working with 3 digit numbers. 

The Common Core standards expect students to count by 10s to 1000, so working with hundreds and correcting misconceptions, is important before students begin to add and subtract with 3 digit numbers.

  Correcting Misunderstandings
  Developing a Conceptual Understanding: Correcting Misunderstandings
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Crossing Over 100

Unit 6: Everything in Its Place
Lesson 12 of 14

Objective: SWBAT count across decades and centuries when working with numbers between 100 and 1000

Big Idea: Students often become confused as they count from one decade to the next. In order to become fluent with operations in addition and subtraction, students need to be able to move across decades.

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