Saturday, October 13, 2012

How to Teach Rounding Using An Open Number Line {CCSS 3.NBT.A.1, 4.NBT.A.3}

Rounding numbers is a math skill that is easy to teach if you train the kids how to circle a number, underline another, apply a rule, etc. Heck, I’ve even patted myself on the back for making up a catchy little ditty which helped my friends to all ace the rounding questions on the state assessment. Unfortunately, that did not mean they understood the concept or that they could apply it to real world situations. It’s important to teach our little friends about what rounding  actually means and to further develop their understanding of the number system.

We round numbers when estimating is a “good enough” option and because rounded numbers are easier to work with in our head. Since rounding “in real life” doesn’t involve a pencil and paper to circle and underline it doesn’t make sense to teach it that way. 

Have you met my friend The Open-Number Line?

We weren’t really all that close at first.

In fact, he kind of rubbed me the wrong way. I like rules and clear cut guidelines. He was far too wild and unpredictable for my taste.

But then I took the time to get to know him better. And I learned we had addition in common. 

Then I had some students who really struggled with subtracting “big” numbers and he was there to lend a helping hand. From that point on I was totally in love.

We’ve been BFFs ever since.

And I really encourage my students to make him a Bestie as well. He is great for oh-so-many concepts...elapsed time....fractions...he’s got it covered.

Rounding is another area in which he excels.

To show your friends how to round, start with rounding to the nearest ten. Draw a number line and label each end with a consecutive multiple of ten (for example 20 and 30). Add a number in the middle (in this case 24). Guide the students to see that 24 is closer to 20 than to 30. Do the same with 27 and guide them to see that it is closer to 30. Explain that when a number has a 5 in the ones place it is exactly in the middle of two 10s, but that we always “round up.”

Once your students are comfortable working with tens, repeat the process using hundreds.
Since rounding is one of the Common Core Standards it is getting far more attention in my classroom than ever before. And so I decided to capitalize on the excitement that is the month of October and created a center and task cards to provide some additional practice for my friends. 
The packet includes activities for rounding to the nearest 10, 100 and 1000 so it is great for differentiating to meet the varied needs os your students. It includes 7 different printables with open number lines to help students practice rounding on a number line. I suggest laminating the mats or inserting them into plastic page protectors and using dry erase markers for initial proactice. You could also use a document camera to teach this as a whole class lesson. It may be helpful for some friends to visualize the number line bent like a hill which is why I included the hill clipart with the number line. I placed one of the pumpkins onto the number to show that the pumpkin would “roll” towards a multiple of 10...or 100...or 1000.

The packet also includes 3 sets of task cards (24 cards each) and a recording sheet. The “task card” format is so much more exciting for students than a traditional worksheet.

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  1. You've been Boo-ed! Hop on over to to check it out! Happy Fall!

    Miss Nelson’s Got the Camera!

  2. I have used a rounding number line for the past 4years and had awesome results. The kids love it and use it for rounding decimals too, we also use it for fractions and elapsed time. We talk about "friendly" numbers when we find the end numbers.

  3. When I first started teaching math (5th grade), I didn't quite get using a number line. It's so easy to take for granted what we know and what we think is easy. But after a while (once you have spent some time with a grade level) you begin to understand how your little people think and what they need. I keep laminated number lines in a bucket handy for all sorts of use. Thanks for the great blog. It's very well put-together and thought out. I would love for you to check out my blog as well.

    keep up the great work

  4. This looks VERY good! I too am right where you once were; we have the chant completely down, and most of my kids can go through the motions of figuring out how to round with it, but I have struggled in wondering, "Do they understand the WHY and not just the HOW of rounding?" Some kids, I'm not so sure.
    I would like to know your WHY with this number line - have you thought of doing a video on uTube demonstrating the teaching aspect of it? That would be helpful to so many teachers, I'm sure!


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