Automaticity addition to 20 crossing tens

General

Students learn to solve addition problems to 20 crossing tens quickly and correctly.

Standards

CCSS.Math.Content.2.OA.B.2

Learning objective

Students will be able to quickly and correctly solve addition problems up to 20 in my head crossing tens.

Introduction

Practice two addition problems as a class. Use the visual support. Make sure to demonstrate calculating with the middle step to the multiple of ten before going on.

Instruction

Explain to students what automaticity is, and what automaticity in addition problems means. Tell students that they are going to practice solving addition problems in their head within a given time. The goal is to solve the addition problem within 5, 4, and even 3 seconds. Start by discussing the three problems, the first in 5 seconds, then 4, and finally in 3 seconds. Then ask students to solve the problems within those times and discuss the answers. Tell students that have trouble solving within time that this is something that improves with practice. Then challenge the class to solve three problems in 15 seconds and four seconds within 20 seconds.

Check that students are able to quickly and correctly solve addition problems to 20 crossing tens by asking the following questions:
- Why is it useful to be able to quickly solve addition problems?
- Can you explain the steps to adding 8 + 4 also using the middle step to the multiple of ten.
- How do you solve an addition problem if you only have 20 seconds to find the answer?

Quiz

Students practice with sets of addition problems and are challenged to complete them in progressively less time.

Closing

As a class stand in a circle and ask one student to go to the middle of the circle. The student in the center of the circle comes up with an addition problem to 20, then closes their eyes and spins in a circle while pointing their hand. The student who they point at has 5 seconds to solve the addition problem. You can increase the challenge of the game by asking students to answer in 4 and then 3 seconds.

Teaching tips

Students who have difficulty with this learning goal can be supported by asking students to solve addition problems to 20 without a time limit. You then can ask students to solve problems with a time limit of 30 seconds, 25 seconds, 20 seconds, etc.