Subtraction to 10 with rekenrek

General

Students learn to subtract numbers to 10 by solving the problems on the rekenrek.

Common core standard

1.OA.A

Relevance

It is useful to be able to solve subtraction problems on the rekenrek so you can see how many beads are taken away and how many beads are left. Learning to use the rekenrek well also helps build mental math skills.

Introduction

Students practice counting of quantities to 10. They count all the the similar objects in the image and jot down their totals. Discuss how many of each object there are and write the totals on the interactive whiteboard.

Development

Ensure that every student has a rekenrek so they can practice along with your explanation. Show students how to recognize the set of 5-bead structure on the rekenrek. There are always 5 red beads and 5 white beads on the top and bottom row. Practice recognizing amounts with the students. Show the rekenreks on the interactive whiteboard and tell students that they should count the beads on the left. Check the answers together and then show a rekenrek with 10 beads. You can see at once that it is 10 beads by using the sets of 5 or skip-counting in 5s, meaning students don't need to count individual beads. You can quickly recognize amounts greater than 5 by using the colors. Practice with this and and ask students to note their answers. Explain that you can calculate subtraction problems using a rekenrek by counting a total of beads on the left, and then moving the beads you take away to the right. The beads on the left side and the beads under the arrow are the first number of your subtraction problem (minuend). The beads that are under the arrow (moved to the right) are the beads that are taken away (subtrahend). How many beads are left? That is the difference. Practice this with a few examples and have students do the subtraction problems on their own rekenreks. Students then practice with subtracting with numbers to 10. They write their answers down which are then discussed as a class and shown on the interactive whiteboard.

Check that students are able to subtract numbers to 10 on the rekenrek by asking the following questions:
- How can you quickly see how many beads are shown on the rekenrek?
- How many beads do you see on the top row of the rekenrek? And the bottom row? How many beads are there together?
- Which way do you move the beads if you take away one number from a second number?

Guided practice

Students practice subtraction with numbers to 10 on the rekenrek. They must carefully look at the beads shown on the rekenrek in the images given.

Closing

Have students work in pairs to practice subtraction on the rekenrek. Make sure that each pair has a rekenrek. The first student comes up with a subtraction problem for the rekenrek and says the subtraction problem aloud. The second student must solve the given problem. They take turns. Remind students that they must show leave space between the first number and the amount to take away, so you can clearly see the how much has been taken away. Practice together by asking students to match the subtraction problem to a rekenrek. Finally discuss that it is useful to be able to subtract with a rekenrek, so you build mental math skills.

Teaching tips

Encourage students who have difficulty with subtraction with numbers to 10 to do all the subtraction problems from the lesson with you on the rekenrek. They can also be helped by working on recognizing amounts on the rekenrek. Then practice with simple subtraction in which only 1 is taken away each time (4 - 1, 3 - 1, etc). Some students may already be able to calculate mentally without using the rekenrek.