# 1. Ten ones equal one ten (C)

## About this lesson

Lesson objective: Understand that ten ones are equal to one group of ten.

Students bring prior knowledge of ten ones from K.NBT.A.1: Compose and decompose numbers from 11 to 19 into ten ones and some further ones. This prior knowledge is extended to grouping 10 ones into a group of 10. A conceptual challenge students may encounter is accepting that 10 ones, or items, can be represented as one unit of ten, and then counted as one group.

This lesson introduces the concept that a bundle of ten ones is called "a ten." This is called unitizing and is foundational to students' ability to count groups as though they were individual objects. Prior to this introduction of unitizing, the experience that students have had counting has related one number said with one object counted. In this unit, students begin to make a shift in their understanding of counting and our place value system. Now students may count "10, 20, 30," saying only 3 numbers but having counted 30 objects. This shift in thinking requires time and rich experiences with concrete manipulatives to develop. Experiences with concrete manipulatives will help to build students in their understanding of number conservation. For this reason, it is important to provide ample time with cubes and other counters on ten frames, rather than using pre-grouped tools like base ten blocks or bean sticks.

The concept is developed through work with counters, representations, and ten frames. This work helps students deepen their understanding of equivalence as they notice that 10 ones are equal to one group of ten, or one ten. Students will continue this work throughout the year as they develop addition and subtraction strategies, compare numbers, and count by tens.

Students engage in Mathematical Practice 7 (Look for and make use of structure), as they repeatedly make bundles of ten using objects and by drawing in ten frames. Students are asked to verbalize the concept that ten ones makes one ten. Visualization of one unit of ten is developed as they see, and work with, various representations in the forms of a box of cupcakes, a ten frame, and other "grouped" objects.

**Key vocabulary:**

- bundle
- group
- single
- ten/ "a ten"
- ten frame

**Special materials needed:**

- cubes or counters
- ten frames (See Additional Materials)