How to Teach Rounding Decimal Numbers

Rounding decimal numbers is a skill all 5th grade students need to have. Unfortunately, an anchor chart isn't going to cut it! Your students need an activity that allows them to understand decimal numbers on the number line. When your students have robust number sense around decimal numbers, rounding decimals will be a breeze! Teaching rounding lessons using this method will ensure that every student in your class is a whiz when it comes to rounding! #Rounding #Decimals #5thGradeMath
A few years back I wrote the post "5 And Above, Give It a Shove... No, Really..."  It's been a few years but when I type "rounding" into Pinterest, 3 of the top 5 results still involve a search for an anchor chart.

Anchor charts are great, but when your students have an understanding of what rounding means and number sense around the numbers they are rounding an anchor chart with a "Rounding Roller Coaster" is just not necessary. At all.

In the original post mentioned above, I describe a method for rounding numbers to the nearest ten. The thing is, that exact same method can be used to round to any place! The difficulty when teaching rounding of decimal numbers to 5th graders is that you need to know where to begin. Some students have no concept of what rounding is while others know what rounding means but don't understand decimal numbers. Some students are missing both of these pieces! Using a number line we can get out in front of both of these major misconceptions to help our students to be successful.

Understanding Rounding 

Step 1 to rounding decimals (or any numbers) is for students to understand that rounding means finding the closest "round" number based on the place being rounded to. I like to play a game called "Find the Hidden Number" to reinforce this idea. 

Even when teaching rounding decimals, I start this activity with whole numbers. I want students to understand rounding and using "easier" numbers allows them to free up the mental space they need to think about rounding- not the numbers they are rounding! 

Here you can see I have a number line with numbers between 0 and 1,000 counting by hundreds. To play "Find the Hidden Number" you will give your students a number and they will point to the spot where that number would be "hiding" on the number line. If you asked your students to find 624 they would need to point between 600 and 700. Then, ask your students which of those hundreds 624 would be closer to. If you find your students can't quickly and automatically tell you the closest hundred, chances are they are nowhere near ready to start rounding decimals- their understanding of whole numbers isn't even solid yet! 

 Decimal Number Sense 

Once your students understand what it means to round by finding the nearest benchmark number, you will want to do number sense building activities around decimal numbers. One activity I love is ordering decimal numbers. I give students a blank number line and the numbers 0 and 1. One at a time, I give students number tiles for the tenths that come between 0 and 1 and ask students where on the number line these numbers would go. One at a time they place these numbers thinking about the scale and placement of numbers between 0 and 1. 

The first time through the activity I do not correct students who place a tile incorrectly. I simply wait for them to get the tile that would go in that spot and let the students notice for themselves that there is a problem with their placement. When students finish, clear the board and play again giving the tiles in a different order. Look for students who start to notice their previous errors and who are able to put the tiles on the board without any corrections throughout the game. This game can be played over and over with numbers between 0 and 1 or even between 0.05 and 0.06. The range is endless and will allow your students to practice understanding decimal numbers. 

A variation on the game after your students are confident with the number tiles is to take the tiles away giving students only the end benchmark numbers and asking them to fill in the decimals that would come between by writing them in themselves. 

Putting It All Together 

Now that your students understand what it means to round and they have number sense around decimal numbers, it is very simple to put the two skills together. Given a number such as 0.81 and asking students to round to the nearest tenth, here's how their thinking would play out. 
  1. Students would first know know "0.81 is between 8 tenths and 9 tenths" by playing "Find the Hidden Number". 
  2. Thanks to the number line activities, students would easily know that 0.81 is much closer to 8 tenths than 9 tenths. 
No rhymes, no anchor charts with roller coasters, no tricks at all. An understanding of rounding and a strong internal number line are all your students need to be successful! 

If you are looking for detailed lesson plans with pictures and examples along with all of the number tiles needed to teach this lesson, I have compiled these resources for you! Head to my TPT store to check it out :) 

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