Third graders are developing mathematical skills and learning to use them to solve problems. Rounding is an important basic number skill to teach these students. They are hands-on learners and appreciate the opportunity to work alone to evaluate their thinking. After introducing the concept of rounding, allow students to work individually or in small groups to demonstrate their understanding of the concept.
Fill water bottles with varying amounts of water.
Ask students whether the water level is closer to the top or the bottom of the bottle. This activity helps students understand the general concept of rounding by allowing children to visualize the concept.
Add labels to the top and bottom of one of the bottles. Label the bottom as "0" and the top as "10." Write the numbers one through nine at equal intervals up the side of the bottle. Make sure the five is in the middle.
Explain that rounding numbers works the same way as the water bottles. Tell students that if a number is five or higher, they round it up to the nearest ten. If it is less than five, they round it down. Explain that rounding allows them to substitute similar numbers that are easier to work with in a given math problem. The water bottles help students visualize that points one through four are closer to "0" and five through nine are closer to "10." The students will see that when the water is at or above the "5," the water is closer to the "10" than it is to the "0."
Repeat with other bottles using different labels. For example, label one with "10" at the bottom and "20" at the top. Try one with "90" at the bottom and "100" at the top.
Let students test their understanding of the concept. Label spaces on a desk with index cards numbered "0," "10," "20," "30," "40," "50," "60," "70," "80," "90" and "100."
Give students number flashcards to sort according to the number they should round it to. For example, 28 and 32 would both round to 30, so students should put them in the same pile.
- ['Water bottles', 'Permanent marker', 'Index cards labeled 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100', 'Number flashcards']
Show students how they can use rounding to check their answers to addition and subtraction problems. For example, if they round "35 + 24" to "40 + 20," they can determine whether the answer they got makes sense.
Skip counting by 10 is an important prerequisite to rounding. Students should be able to proficiently skip count by 10 before you introduce the concept of rounding.
- water bottle image by Radu Razvan from Fotolia.com