standard_description: Fluently add and subtract within 20 using mental strategies. (See standard 1.OA.6 for a list of mental strategies.) By end of Grade 2, know from memory all sums of two one-digit numbers.
problem_activity: Narrative
The purpose of this activity is for students to describe patterns in the sequence of even and odd numbers when they count by 1. Students notice that even numbers are numbers that you count when you skip-count by 2 (MP7).
In order for all students to visualize the sequence, perform the activity where the whole class can be arranged in a circle with space for students to sit and stand. Depending on class size, the count may go beyond 20. It is ok for students to notice and wonder about even and odd numbers beyond 20, but maintain the focus throughout the lesson on numbers within 20.
Launch
Form the class into a circle with all students standing.
“We are going to count together by 1. The first person to count will say 0 and stay standing.”
“The next person will say their number and sit down. The next person will say their number and stay standing.”
“We will keep counting until everyone has said a number.”
As needed, demonstrate the stand-sit-stand-sit sequence.
Record the count:
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Prompt students who are standing to say their numbers. (0, 2, 4, …)
Prompt students who are sitting to say their numbers. (1, 3, 5, …)
Activity
“Write down what you notice and what you wonder about the numbers in our count.”
3 minutes: independent work time
2 minutes: partner discussion
Monitor for students' responses that focus on even and odd number patterns to share in synthesis.
Student Facing
What did you notice? What do you wonder?
Student Response
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Activity Synthesis
Share and record student responses.
Display:
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“This is a list of all the even and odd numbers from 0 to 20.”
“What patterns do you notice?” (All the even numbers are numbers you say when you skip-count by 2. The digits 0, 2, 4, 6, 8 repeat in the ones place for even numbers. The digits 1, 3, 5, 7, 9 repeat in the ones place in odd numbers.)
“How could you use these patterns to tell if a number of objects is even or odd?” (If the number is an even number you say it when you skip-count by 2.)


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