Rounding Background Information for Teachers, Parents and Caregivers
This page provides information to support educators and families in teaching K-3 students about rounding. It is designed to complement the Rounding topic page on BrainPOP Jr.
This movie will introduce estimation and rounding and explain how to round numbers to the nearest tens and hundreds place. We recommend watching the movie and exploring the features over the course of a week or more. You may want to watch the movie again after children are more familiar with the skill and then stop the movie when there is a number on the screen. Encourage children to round the numbers that are on the screen before Annie and Moby do!
Review with children that when you estimate, you use what you know or see to make a reasonable guess about an amount. Estimate different amounts together, such as the number of books on a shelf, number of marbles in a bowl, or the length of a desk. Go through reasonable and unreasonable estimates together. Explain that when people estimate, they round numbers to make them easier to work with. This means changing numbers so that they end in a zero (or several zeroes).
Show the number 38 on a number line from 30 through 40. Guide children to see that 38 is closer to 40 than it is to 30. So, we round 38 up to 40. Then show the number 31 on the number line. Help children see that 31 is closer to 30 than to 40. So, we round 31 down to 30. Then show the number 35 on the number line. Some children may point out that the number is right in the middle between 30 and 40. Explain that when a number ends in 5, it is right in the middle of two tens, and we round up. So, 35 rounds up to 40. If a two-digit number ends in 0, then it is already rounded to the nearest ten!
To show children how to round without a number line, present a number to children and point out the ones place. Explain that when you round to the nearest ten, you look at the digit in the ones place to help you decide whether to round up or round down. If the digit is less than 5, you round down to the nearest ten. If the digit is 5 or greater, you round up to the nearest ten. It may be helpful for children to imagine a hill with the numbers 1 through 10 going up and over the hill, with the 5 at the top of the hill. When you reach the top of the hill (5), it’s easier to go over to the higher number (10). Practice different examples together using number lines, hundred charts, and/or place value charts.
After children feel comfortable with rounding to the nearest ten, challenge them to round to the nearest hundred. Show the number 413 on a number line between 400 and 500. Which hundred is 413 closer to, 400 or 500? Help children see that 413 is closer to 400, so we round 413 down to 400. Then present 489 on the number line. Ask children if they should round the number down to 400 or up to 500? Why? Repeat the activity with 450. Remind children that when a number is right in the middle between two numbers, they should round up. Explain that when they round to the nearest hundred, they look at the digit in the tens place to help them decide whether to round up or round down. If the digit in the tens place is less than 5, round down. If the digit in the tens place is 5 or greater than 5, round up. If there are zeroes in the tens and ones places, then the number is already rounded to the nearest hundred! Round different three-digit numbers together and have children explain how and why they rounded up or down.
Discuss with children why rounding numbers might be useful. Challenge children to come up with numbers and have partners round them to the nearest ten or hundred. Give plenty of opportunities where children can practice the skill and become experts!
