Rhymes and the Rounding Roller Coaster

The program my district uses starts third grade with lessons on rounding. This year I received inquiries from a few schools asking if it was ok to spend a few more days on rounding to the nearest ten and then a few days rounding to the nearest hundred. Every year students struggle to round and teachers resort to pulling out rhymes and their pictures of the rounding roller coaster.

While mnemonic devices can be helpful, rhymes can sometimes create more confusion. Here are two common examples found online:

4 or less

Let it rest!

5 or more

Let it soar!

Neither of these rhymes mentions anything about which place value these rules apply to or what to do with the digits to the right of the place to which you are rounding.

This rhyme explains what to do with those digits but it does little to build conceptual understanding. It won’t help at all if a kid can’t remember the rhyme or which direction to look “next door.”

Find your place

Look next-door

Five or greater,

Add one more

All digits in the front stay the same

All digits behind, zero’s your name

Strengthening Number Sense

So what’s a better way to teach rounding?

Using chunks of the number line can strengthen students’ understanding of rounding. Number lines help students develop a visual image of number magnitude and order. Let’s start by rounding 27 to the nearest ten. First, we need students to identify the tens that “bookend” the number 27 by asking “What two tens does 27 fall between?” Once they identify that it falls between 20 and 30, I would draw an open number line with those two numbers identified.

I would then ask them to help me mark 27 in the correct place, using the halfway mark, 25 as a benchmark. Visually, it would be easy for them to see that 27 is closer to 30 and would therefore round to 30.

This strategy, once learned, would stay with students long past an easily forgotten rhyme. You might ask how a rounding roller coaster is different. After all, it’s just a curved number line, right? In my experience, the rounding roller coaster usually doesn’t have equal distances between each number like a number line should. If you have one that does and the middle is the halfway point, great. If you’re looking for another way to develop number sense, read on.

Bookends

In addition to lacking a strong visualization of numbers on a number line, one of the things that I see that causes difficulty for students when rounding to larger numbers is the inability to correctly identify the bookend numbers. If, for example, they are asked to round 243 to the nearest ten, they might say that the two tens that 243 falls between are 200 and 300 instead of 240 and 250. I see this become more of a struggle as they progress to larger numbers, especially when rounding to smaller place values, e.g. 1,629 rounded to the nearest ten.

You can strengthen this skill by asking students to give you the bookends for a given number when you have a few extra minutes, such as when you are lining up or waiting for dismissal. You might give a student a number like 841 and ask them for the two hundreds or tens that it falls between.

Finding Bookends Activity

Here’s a way to get students up and moving while providing some practice identifying those bookend numbers. Create sets of index cards where each set will have a pair of bookend numbers and one or more numbers that will fall between those bookend numbers, depending on the number of students in your class. Try to make them unique to avoid confusion as students try to find their group. Pass the cards out randomly and have students find the students who have the other cards in their set.

Here’s a set of 2-digit numbers to get you started! Make a copy of this Google Doc and edit for 3-digit numbers or decimals.