How to Teach 3rd Grade Rounding and Estimation Using Number Lines
There are many good strategies for teaching rounding and estimation in 3rd grade math. One of the most common rounding strategies is the roller coaster method, where students look at the digit in the ones place and round down or up according to the rule.
While this method does work, using number lines can really help students grasp the true concept of rounding instead of just memorizing rules.
In this blog post I’ll share:
How to teach rounding using number lines
What to do when the number falls right in the middle
Teaching estimation by finding the greatest common place value
Let’s jump right in!
How to teach rounding using number lines
When planning your 3rd grade rounding lesson, students first need to be introduced to these vocabulary words: rounding and round number. A round number is a number that ends in zero (10, 20, 30, 40, 50 and so on).
The definition of rounding says to find the nearest ten, hundred, or thousand. Number lines are a great way for students to visually see what a particular number is closest to (nearest). Let’s look at the example below:
Students first locate the number on the number line, and can quickly see that 454 is closest to 450 and 3,217 is closest to 3,220. Therefore, 454 rounds to 450 and 3,217 rounds to 3,220.
What to do when the number falls right in the middle
So how do we teach students what to do when the number falls right in the middle? Explain to students that when rounding, there is one important rule to remember. Just like we follow rules when we drive a car (stopping at a stop sign for example), we must follow this rule when rounding: When the number falls directly between two tens (when the ones digit is a 5), we always round up!
Teaching estimation by finding the greatest common place value
After students have mastered rounding, it’s time to teach estimation. Explain to students that an estimate tells about how much or about how many, and rounding is just one way to estimate (it has rules).
When given several numbers, each with a different number of digits, we look for the greatest common place value to determine whether to round to the nearest ten or hundred.
Let’s see this in practice with a 3rd grade word problem that involves estimation:
Explain to students that the greatest common place value is the tens place, so we round to the tens. $748 is about $750, $350 is already a round number, and $62 rounds to $60 so Destiny will have about $460 left.
You can see the importance of introducing the terms round number and rounding at the beginning of the lesson so you can better explain the process of estimation to students. While other strategies for teaching rounding do work, using number lines as a visual representation for determining whether or not to round up or down really works well!
If you are interested in teaching rounding and estimation using this strategy in your 3rd grade math class, be sure to check out my rounding and estimation powerpoint lesson! The interactive slides will keep your students super engaged, and all you have to do is download the presentation and teach!
RELATED POSTS:
How I had 100% Passing 2nd Grade Math in Just Two Short Months My First Year Teaching
Ditch Calendar Math for These 3 Engaging Elementary Math Routines
5 Hands-On Activities to Teach 2nd Grade Multiplication & Division
