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 fine for students to notice and wonder about even and odd numbers beyond 20, but maintain the focus throughout the lesson on numbers within 20.

• Share and record student responses.
• Display:

  

• “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. Look at the ones digit. If it’s 0, 2, 4, 6, 8, the number is even. If it’s 1, 3, 5, 7, 9, the number is odd.)

The purpose of this activity is for students to make and test conjectures about the effect of adding 1 and adding 2 on the parity (being odd or even) of a group of objects. Students use what they know about equal groups, pairs, and skip-counting to explain why adding 1 may change whether a group of objects is even or odd and why adding 2 will have no effect (MP3, MP8).

• Display student conjectures from the Launch.
• “Let’s use Jada’s counters to show which of our ideas are true.”
• Invite students to share how they filled in the row about Jada’s counters.
• Display:

• “How do these equations show that adding 1 changes whether a number is even or odd, but adding 2 does not?” (You can see 2 equal groups of 8 in each. 17 is odd because there is one left out. 18 is even because you have 2 equal groups and 1 pair. You could give each group 1 to make it .)