Teaching rounding with open number lines and place value skills so 3rd grade and 4th grade students actually understand

Teaching Rounding So Students Actually Understand

Teachers use all sorts of tricks to teach students how to round - tricks like rollercoasters, chants, step-by-step anchor chart instructions, underlining digits, and more. Teaching rounding using tricks is a short term solution, though.  If you are having to use tricks in order for students to understand rounding, then your students are showing you that they have some gaps in their place value understanding.

teaching rounding so your 3rd grade and 4th grade students actually understand - with open number lines and place value understanding

Rounding essentially boils down to which number is closest.  If your 3rd grade student doesn't know that 137 is closer to 100 than it is to 200, then teaching a special trick instead of addressing their place value gap is hurting them in the long run.

Teach Rounding Using Open Number Lines

Teaching students to round using open number lines is a much better long term plan.  This will not only help them with their rounding skills, but it will also help strengthen their place value understanding.  They will be able to use what they have learned about creating open number lines as they progress to more difficult math.

An open number line is simply a number line that starts off empty.  Students fill in the number line and build on it based on the problem they are trying to solve.

If students have the ability to draw out an appropriate open number line when rounding, they will easily be visually see what number is closest.  Rounding will be easy!

Scaffolding to the Open Number Line to Help Students Be Successful

Having students start using and creating their own open number lines without any scaffolding will most likely be frustrating to your students, especially if they struggle with place value.  I have found that students struggle most with determining the midpoint between two multiples, and determining what two multiples (of ten, hundred, thousand, etc.) a number is in between.  Before jumping into open number lines, provide scaffolded, partly filled in number lines to help your students better understand these aspects of rounding.

This might take a little longer than teaching students a quick trick, but the place value skills it reinforces are invaluable, especially as students tackle more difficult math.

Determining the Midpoint Between Two Multiples

Have students practice labeling midpoints or halfway points on number lines where the multiple of ten, hundred, thousand, etc. is already provided for them.  Start with numbers less than 100, then gradually get to larger numbers.  Some examples are provided below.


Determining What Multiples (Of Ten, Hundred, Etc.) A Number is In Between

Provide the midpoint and another number for context, and then have students label the multiples that a number falls between.  Some examples are provided below.  Just like above, start this activity with numbers less than 100 and then gradually increase to larger numbers.  This will help you identify where exactly your students struggle.


Once students are able to do these two activities successfully, then they probably have the place value foundation to be successful rounding using open number lines.

Now, students just need some guidance drawing their own number lines when rounding. Model how you would draw your own number line in order to solve different rounding problems before expecting the to do it independently.    They will also need some instruction on how to round the midpoint since it is equally close to both sides.

How to Help Students Whose Place Value Skills Are Lacking

If they are not able to do these two activities, then they will need practice with different place value skills, depending on where they struggle.  Sometimes, students just need a little more scaffolding and practice before moving on.  Have them practice filling in missing pieces on all sorts of number lines.  This will help them build a foundation for all sorts of skills, not just rounding.

I have found that most students that were struggling were actually able to do these activities using smaller numbers.  This told me that my students had a solid foundation for numbers less than 1,000, but needed practice with numbers greater than 1,000.

To build place value understanding for numbers greater than 1,000, do the same things you would do to practice smaller numbers.  Practicing counting by different multiples is an easy, no prep activity that can be done anytime you have an extra couple of minutes or you are waiting in the hallway. For example,

  • count by 1s starting at 3,589
  • count by 10s starting at 2,000
  • count by hundreds starting at 60,200
  • count by thousands starting at 77,400

You should do activities like this both orally and written. You might be surprised at how your students struggle with counting numbers larger than 1,000 - even counting by 1s - when they have to write it out.   (This is a great activity for whiteboards.)

If you think your 3rd grade or 4th grade students could use some extra scaffolding as you teach rounding, then see if my Rounding to the Nearest 10 and Hundred Bundle would fit their needs.

This resource includes hands on, scaffolded activities to help your student become successful rounders.  It starts small, starting with numbers less than 100, and gradually builds to larger numbers.  Students practice finding midpoints, labeling different parts of a number line, identifying the multiples of ten, hundred, or thousand that a number falls between, and more.

The resource leads students to draw their own number lines and eventually to round without any number lines at all.

It also includes fun whole class activities - snowball fights and scavenger hunts - as well as independent activities and activities that could be done in centers.

You can also use this resource to help you differentiate.  Your struggling learners might need to start with the basics, while your learners that already have a solid understanding of rounding can do the more advanced activities.

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