Lesson 21

This warm-up prompts students to carefully analyze and compare arrangements of 11–19 images. 

• Groups of 2
• Display the image.
• “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

• “Discuss your thinking with your partner.”
• 2–3 minutes: partner discussion
• Share and record responses.

• “Let’s find at least one reason why each one doesn’t belong.”

The purpose of this activity is for students to compose and decompose numbers 11–19 as 10 ones and some more ones. Students work with groups of 11–19 objects to represent a context about students in a classroom where there is room for 10 students to sit at a table and the rest of the students sit on a rug. To solve the problem, students may count the total number of objects and then find a group of 10 or they may start by putting 10 objects at the table and see how many cubes are left on the rug and count all, count on, or know the total without counting. They record the two groups and the total by filling in equations.

Students work with multiple collections of 11–19 objects. They can be given access to a variety of collections of objects to choose from and then switch collections with other groups.

• Each group of 2 needs access to at least 2 collections of 11–19 objects.

• Groups of 2
• Give each group of students access to collections of 11–19 objects.
• “We are going to pretend that the objects in the collection are students.”
• “The students will either sit at the table or on the rug.”
• Display the image.
• “All of the students want to sit at the table. How many of the students can sit at the table?” (10 students)
• 1 minute: independent work time
• “10 students can sit at the table. The students who do not fit at the table will sit on the rug.”
• “Work with your partner to figure out how many students will sit at the table, how many will sit on the rug, and how many students there are altogether. Fill in an equation for each bag of objects.”

• 7 minutes: partner work time

• “The collection Jada is working with has 14 objects. She showed 10 students sitting at the table. How many do you think will be still on the rug? Why do you think that?” (4, 10 and 4 is 14)

The purpose of this activity is for students to compose and decompose numbers 11–19 as 10 ones and some more ones in the context of filling in equations with a missing addend. Students may just know the numbers needed to make numbers 11–19 with repeated experience or they may use objects like connecting cubes and two-color counters to represent the equations. This activity is optional because the standards do not require students to fill in equations with one missing addend in kindergarten.

• Students can use their bead tool from a previous lesson.

• Groups of 2
• Give students access to connecting cubes or two-color counters, 10-frames, and bead tools.
• Display the student book.
• “Kiran wrote equations to show the total number of students and how many students sat at the table and how many sat on the rug, but he didn’t finish the equations. Finish filling in each equation. You can use connecting cubes or two-color counters if they are helpful.”

• 4 minutes: independent work time
• 4 minutes: partner work time
• Monitor for students who:
  • count out the total number of objects and then determine the two parts.
  • just know the parts to make teen numbers.

• Invite students who used objects to share.
• Invite students who just knew the missing number in the equation to share.
• “What is the same about each equation? What is different?” (They all have 10. Sometimes the total number of students is on the left and sometimes it is on the right.)

The purpose of this activity is for students to choose from activities that offer practice with number and shape concepts. Students choose from 5 centers introduced in previous units. Students can choose to work at any stage of the centers.

• Shake and Spill
• Number Race
• Grab and Count
• What's Behind My Back?
• Pattern Blocks

• Gather materials from:
  • Shake and Spill
  • Number Race
  • Grab and Count
  • What's Behind My Back?
  • Pattern Blocks

• Groups of 2
• “Today we are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Think about what you would like to do first.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice.
• 8 minutes: center work time
• “Choose what you would like to do next.”
• 8 minutes: center work time

• “What can you do when there is a math problem or center that you’re not sure about?”