ordering numbers to 120 on an open number line
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Ordering Numbers on an Open Number Line

An open number line—one that isn’t labeled with numbers—is a great tool with many applications in the math classroom. The power of an open number line is that you write in only the numbers you need. Here you see an example of using an open number line to add.

adding on an open number line

Notice that in the example shown above, the spacing approximates the magnitude of the numbers. Sure, the jump of 20 probably ought to be a little bigger, but it’s a good attempt and it’s not necessary to be exact.

In Texas, the 1st grade standards have students using an open number line to order numbers to 120. This can be tricky for kiddos, because they need to place the numbers on the number line themselves. The key is helping them understand and use benchmarks.

I recently wrote about flipping the I Do/You Do/We Do script. Let me tell you, it’s been a very popular post! This lesson is a good example of doing just that.

Display an image like the one shown and ask students: Talk to your partner. What number do you think the question mark represents? Be ready to explain your thinking. Facilitate a discussion allowing pairs of students to share their reasoning. If students can understand that 10 is halfway between 0 and 20, it will help them place additional numbers on the number line. Also, although the standard specifies up to 120, I’m starting with smaller numbers.

0 to 20 number line

Now challenge the students to place additional numbers on the number line: Talk to your partner. Where would you place the numbers 8 and 14 on the number line? I specifically chose these numbers. Will they see that 8 should be pretty close to 10? And 15 is in the middle between 10 and 20. Will any of the students think to use that to place 14?

placing numbers on an open number line

You could make this a daily warm-up activity by creating a number line with rope or clothesline. Fold cards in half with numbers on them, and hang them over the rope. Have a few numbers each day and call on students to place them on the number line.

ordering numbers on a clothesline

After working with numbers within 20 for a while, change the magnitude of the numbers, but basically repeat the exercise. You might try 0-50 next, then 0-100, and finally 0-120.

Check out this post to grab a FREE workstation activity for ordering numbers to 120 on a number line.

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