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 choose from a variety of collections of objects and then switch collections with other groups.

• “La colección con la que Jada está trabajando tiene 14 objetos. Ella mostró 10 estudiantes sentados en la mesa. ¿Cuántos creen que están sentados en la alfombra? ¿Por qué creen eso?” // “The collection Jada is working with has 14 objects. She showed 10 students sitting at the table. How many do you think are sitting on the rug? Why do you think so?” (4, because 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 an unknown addend. Students may know from experience the numbers needed to make the numbers 11–19, or they may use objects, such as connecting cubes and two-color counters, to represent the equations. This activity is optional, because the kindergarten standards do not require students to fill in equations with one unknown addend.

• Invite students who used objects to share.
• Invite students who “just knew” the unknown number in the equation to share.
• “¿En qué se parecen las ecuaciones? ¿En qué son diferentes?” // “What is the same about each equation? What is different?” (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 five centers introduced in previous units. Students can choose to work at any previously introduced stage of these centers:

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

• “¿Qué pueden hacer cuando tienen dificultades en un problema matemático o en un centro?” // “What can you do when you’re not sure about a math problem or a center?”