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Tuesday Teacher Tips: Using the Open Number Line

Welcome to the Tuesday Teacher Tips series! Each week we’ll highlight teaching and learning resources, ideas to use in the classroom, as well as things to ponder as you go about your teaching day.

I teach third grade, and the unit we’re currently working on is one that many students struggle with—money, specifically using mental math to count change. There are so many students that just don’t “get” this concept and it becomes very frustrating because they don’t have a developed sense of number relationships. For them, visual representations are essential.

One tool that works well is DreamBox’s Open Number Line. It starts out as a blank line where you decide the numbers to use. In a classroom demonstration, this allows me to “think aloud” to my students and show them what I’m “seeing” in my head as I think through the problem; I’m able to visually model my mental math strategies.

I set up the scenario that I was shopping at a store last night. The cashier added up my purchases and they totaled $00.64. To pay, I gave the cashier a one dollar bill. I ask, “How much change did I receive?” 

To demonstrate my strategy on the number line I type in 64, the purchase total, and explain, “Since tens are so much easier to add in my head, I want to figure out how much I need to get to the next dime. Six cents takes me up to 70 cents.” I add 6 as my addend to 64 on the number line. “Now I need to get up to a dollar or one hundred cents. That’s 30 cents.” I add 30 to 70 on the number line and point out the arcs. “So I added 6 to get to 70, and 30 to get to 100. Now I add 30 + 6, easy numbers to add in my head. The cashier gave me thirty-six cents back.” 

This works great as the main lesson or as a warm-up to reinforce the skills of mental math and making change. 

Do you have an effective visual that you use with your students to teach mental math strategies? Please share, we’d love to hear about it and pass the word to other teachers!

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