Rounding: Part 2 How to Teach Rounding within 100 effectively

As I mentioned in my post on Why Teach Rounding, rounding is an incredibly useful tool to help children to compute answers easily and also, if taught effectively, to develop their underlying number sense. In this post, I am going to set out what I mean by effectively, some of the common difficulties that children encounter and some simple steps that can really support children.

Hold off on the rhyme

I'm sure you've heard of lots of rhymes to help with rounding like "5 to 9 climb the line; zero to four, stay on the floor."

I am a great fan of rhymes to help teaching maths facts and skills (see my post on skip counting rhymes), but here, I would strongly suggest waiting until children have thoroughly understood the concept and can round, either independently or with a scaffold.

There are a couple of reasons why:

1) I have noticed children might know the rhyme when we learn it but find it hard to apply it when we have left rounding for a while.

2) For children with memory or processing difficulties, knowing the rhyme does not equate to understanding what it means.

Have your number line(s) ready

I have specific number lines that I created and I call them rounding rulers. There are 2 things that distinguish them from from 'normal' number lines. Firstly, the midway point, the 5 is well marked and visually highlighted. Secondly, it is very clear what the two "bounding" round numbers are; e.g. 43 lies between 40 and 50. This is to avoid the common pitfall I mention below. You can of course, use a normal number line.

Maths Talk

Start off with your maths talk. Ask children if they know what round numbers are. If they don't, explain that it means numbers ending in zero or zeros. Ask them to discuss why we might use them. You are trying to elicit understanding that it is far easier to add 2 round numbers, than numbers that aren't round; i.e. it is far easier to add 50 and 30, then 48 and 33. Rounding allows us to estimate answers easily.

Lies Between!

You want children to know what multiples the numbers lie between; so for example 37 is between the two round numbers 30 and 40. You then ask children very simply to see is it nearer 30 or 40. On my number lines (my rounding rulers), I make sure the 5 is very clearly highlighted as the midway point or what I call the anchor number. Doing this allows children to very clearly see which one it is closer to. Children can easily and clearly see that 37 is physically closer to 40.

Likewise, when rounding 72, children can see it is between 70 and 80 and that it is closer to 70, so we round it down.

Rounding 5

When numbers end in 5, it can be a bit more confusing. I ask children which they would round it to. Invariably, some go to the earlier multiple and some to the later. I explain that they are both correct, as neither is closer but that the convention I use is that we round up. One child I taught made sense of this by reasoning out that this is because we count forward.

Common pitfall

When rounding down children can often skip the nearest round number. When asked to round 61 down, it is not uncommon for children to round it to 50. This is why it is particularly useful to use visuals and ask the question "What round numbers is it between"?.

The importance of scaffolds

For children who are struggling with rounding, keep using the scaffolds (i.e. your number lines) and keep asking the question, what numbers is it between. If using your own number lines, mark the 5 as the midway point. In my experience, this makes a huge difference for children who find rounding tricky.

What next?

Once children are confident rounding within 100, the next step is to extend this understanding to larger numbers. In my next blog post, Rounding Within 1,000, I’ll look at how to build on the same approach when rounding to the nearest 100 and the nearest 10.

Ready to use Rounding Pack

If you would like to use this approach in your own classroom, I have put together a Rounding Pack with ready-to-teach slides, practice activities and practical scaffolds, including the Rounding Rulers used throughout this post. This can be found in my tpt store.