The purpose of this activity is for students to extend their understanding of teen numbers as a ten and some ones to an understanding of all two-digit numbers as some tens and some ones. Students choose two number cards and create a two-digit number. As they build the two-digit numbers with towers of 10 and singles, students see that each two-digit number is composed of a number of tens and a number of ones (MP8).

Students may read the two-digit number and count out towers of 10 and singles until they have made the number. For example, they may read 82 as eighty-two and count by 10 to 80 and count on by one to 82. Students may think about the meaning of each digit and take that many tens and ones to make the number. For example, they show they know the digit 8 in 82 means 8 tens and the 2 means 2 ones, so they grab 8 towers of 10 and 2 singles.

During the Launch, the teacher demonstrates how to make a two-digit number using number cards and explains how students record their thinking. However, the teacher shouldn’t demonstrate making the number using the connecting cubes, drawings, or _____ tens _____ ones. It is important for students to explore these representations during the activity.

• Display the number 24 and a base-ten drawing of 4 tens and 2 ones.
• “Tyler made a drawing of 24. Do you agree with how he showed 24? Why or why not?” (No, because he drew 4 tens and 2 ones instead of 2 tens and 4 ones. He made the number 42 instead of 24.)
• “Tyler’s drawing shows 42, not 24. They both have the digits 2 and 4, but they are in different places, which makes them different numbers.”

The purpose of this activity is for students to think about the value of tens and ones and consider a representation where the tens are not presented to the left of the ones. In the previous activity, students saw that the order of the digits matters when writing a two-digit number.

In this activity, students see that although the order matters when writing a number, the position of tens or ones in a drawing or diagram does not change their value. Students should have access to connecting cubes in towers of 10 and singles. They should be encouraged to use them if they have difficulty making meaning of the base-ten diagram in their student book.

During the Activity Synthesis, the teacher emphasizes the value of the units in the diagram and the digits and connects them to the commutative property.

When students decide who they agree with and explain their reasoning, they critique the reasoning of others (MP3).

• Invite previously identified students to share.
• Display 68 and 86.
• “When I look at these 2-digit numbers, the order of the digits matters. The order helps me say the number. However, when showing 2-digit numbers with drawings, it doesn’t matter whether the tens or the ones come first. There are still 8 tens and 6 ones.”

The purpose of this activity is for students to choose from activities that offer practice counting, adding and subtracting within 20, or adding and subtracting with multiples of 10. Students choose from any of the previously introduced stages of the listed centers. They are encouraged to choose the center that will be most helpful for them at this time.

• Counting Collections
• Shake and Spill
• How Close
• Check It Off

• Display 9 red counters and put 8 yellow counters under a cup.
• “Mai is playing Shake and Spill with 17 counters. How many yellow counters are under the cup? How do you know?”