Reflection: Student Led Inquiry Building Block Percents - Section 2: Warm up


When I started inviting students to share multiple methods I understood why it takes my students so much more time. Some methods they share, like Molly's work just fine in some situations, but not in others and have the potential to cause serious mistakes.

In the case of Molly's strategy, I was really happy when she shared it. It is one that my students use and misuse a lot. Her explanation gave us the opportunity to examine when it will and will not work. To find 10% of $6000, Molly just cut off the last zero. When students see a strategy like this they can use it to calculate 10% of any whole power of 10. My concern is that my students misuse this strategy when finding 10% of a number like 32.0. Some also get stuck when asked to find 10% of an odd number.

Two other strategies had already been shared by Angelina and Cristina, the decimal slide and equivalent fractions (These videos are linked in the narrative for this section). To avoid future errors,  I decided to ask my students to compare the strategies and decide what was the same about them. I was pleased that my students realized that Molly's way was a shortcut for Angelina's decimal slide, but since the decimal wasn't visible it looked different. I had students to discuss Which method is more generally useful. I asked, "Are there numbers for which one strategy is better than the other?" Eventually, I provided a counter example to help students refine their thinking.

It took time and effort to help my students make these connections, but it was well worth the effort. I feel confident my students possess a better understanding and they have learned to reason with percents more flexibly.

  Student Led Inquiry: Confronting potential misconceptions
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Building Block Percents

Unit 8: Exploring Rational Numbers
Lesson 17 of 20

Objective: Students will be able to calculate any whole number percent of a number mentally.

Big Idea: From 10% students can build 30%, 120%, 5%, etc.

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Math, Number Sense and Operations, percent of a number, Mental Math, rational numbers
  60 minutes
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