Why is Rounding Numbers to the Nearest 10 and 100 So Hard?

Why is rounding numbers to the nearest 10 and 100 so hard for our kids?  Every year I found that my students really struggled to understand how to round numbers. It didn’t seem to matter whether the number was a 2, 3, or 4-digit number. They just didn’t get it. I would teach the standard for rounding every year and knew that it would take longer than the time allotted by our curriculum map – because they just needed more time to get it.

Why It’s Hard

I think it really comes down to number sense – or lack thereof.  I found that incoming third graders could count to 120 by 1’s, and to 100 by 2’s, 5’s, and 10’s. I knew most of them had some experience adding and subtracting using a number line, but I wouldn’t say they were confident.  

I know this because I teach rounding using number lines. It became clearer every year that they struggle with rounding because they don’t have a concrete, conceptual understanding of numbers on a number line, which means it’s a place value problem.

For example, if I ask a student to locate where the number 78 is on a number line and they can’t do it – at least not quickly and without assistance. I know what I need to do.

Start with Place Value

Before we practice with number lines, I like to review place values for ones, tens, and hundreds. A good way to do a quick review is using whiteboards. 

Write the number 237 on the board. Ask students the following questions:

• What number is in the hundreds place?
• What is the value of the 3?

• Which digit has a value of 200?

As you ask the questions, have students write the answer on their whiteboard. Count down 3 – 2 – 1 and have students hold up their whiteboards.

Make a note of who has it and who doesn’t. Continue until you feel you have enough data.

If you have students who need additional help with place value, small group remediation is the way to get them up to speed. In this post, A Place Value Game Your Students Will Beg You to Play I show you a place value game that will help your students get what place value is all about, and they seriously LOVE this game!

Making and Using Number Lines

For kids to understand rounding to the nearest 10 and 100, they have to grasp the concept of numbers on a number line. The concept of where numbers are located is where I start the lesson.

Here is the lesson:

1. Give students a blank number line marked 0 – 100.
2. Model how to label all the tens and fives (benchmark numbers)
3. Write 2 – 3 numbers between 0 and 100 on the board. Ask students to locate them on the number line and add them.

After the lesson:

1. Collect the number lines from your students.
2. Sort the number lines into 1) those that marked all three numbers correctly, 2) those who marked 1-2 correctly, and 3) those who did not mark any numbers in the correct locations.

Why Do We Round Numbers to the Nearest 10 and 100?

Now that you have reviewed place value and number placement, we need to teach students how to round numbers to the nearest 10 and 100. First, they need to understand why we round numbers.

“Rounding big numbers makes them easier to use.”

Here is an example I like to use to explain why rounding is necessary:

This is an example that kids can relate to, so it works!

Benchmark Numbers

One of the easiest strategies for rounding is to teach benchmark numbers. Benchmark numbers are in multiples of 5. They are easy to remember and use in computation. Ex. 5, 10, 15, 75, 90.

These numbers make it easy for students to decide to round up or down because they are the benchmark numbers.

Here is the rounding rule:

Rounding Numbers Practice

Now that your students have practiced using number lines and have the rounding rules – they are ready to use this knowledge in practice. I want my students to use number lines when rounding until they don’t need them anymore – and they’ll know when they don’t.

I plan 5-7 days of rounding instruction and practice that begins with 2-digit numbers rounded to the nearest 10 and progresses to 4-digit numbers rounded to the nearest 100. It includes procedural practice, so they know how to round by using the Rounding Rules. It also includes practice applying their knowledge to word problems that require them to round 2-, 3-, and 4-digit numbers to solve.

These Rounding to the Nearest 10 and 100 Worksheets give them challenging, but guided practice deepens their understanding of rounding by using and finding benchmark numbers.

Math Centers Rounding Numbers Practice

Rounding activities in math centers are an effective way for students to practice their newfound rounding knowledge! These Roll and Round Worksheets are perfect for that.

Throughout this time of practice, I take formative assessments daily.

Why? “Remember – rounding is hard.” I want to be able to scaffold learning for those who need it – but also to stop when they don’t.

More Challenging Practice Rounding Numbers

This set of rounding worksheets also includes activities for students who need to move on to more challenging practice:

• Write 3 Numbers to the Nearest 10 & 100
• Rounding Challenges to the Nearest 10 & 100
• R.U.S.E. – Read, Underline, Solve, Explain Word Problems

Differentiation also means I need to make available activities that challenge those who get it quickly. That’s why I like to use these Rounding Error Analysis Task Cards in a math center. Error analysis is challenging but also fun! It builds mathematical muscle.

This Rounding to the Nearest 10 and 100 Activities Resource is no-prep and full of activities you can differentiate for your 3rd-grade students! Included in this resource is a digital version, which makes it versatile and flexible!

I hope this post helps you teach rounding and make it much easier for your students to master!