Topic D closes the module with students renaming ten as a unit: a ten (1.NBT.2a). This is the very first time students are introduced to this language of ten as a unit, so this is exciting! The unit of ten is the foundation for our whole number system, wherein all units are comprised of ten of the adjacent unit on the place value chart. In Lesson 26, students take a walk down memory lane to revisit representations of 10 ones worked with in the past. They rename their Rekenrek bracelet, the ten-frame, the fingers on two hands, and two 5-groups as 1 ten. They connect teen numbers to the unit form, e.g., 1 ten and 1 one, 1 ten and 2 ones, and represent the numbers with Hide Zero cards. They now analyze the digit 1 in the tens place as representing both 10 ones and 1 unit of ten, further setting the foundation for later work with place value in Module 4 and beyond. Students use their very own Magic Counting Sticks (their fingers) to help them bundle 1 ten. By bundling 1 ten, students realize that some ones are left over, which clarifies the meaning of the ones unit (1.NBT.2b). In Lesson 27, students solve both abstract and contextualized result unknown problems (1.OA.1). The lesson takes them through a progression from problems with teens decomposed or composed using 1 ten and some ones to problems wherein they find the hidden ten, e.g., 8 + 6 or 12 – 5. In Lesson 28 students solve familiar problems such as, “Maria had 8 snowballs on the ground and 5 in her arms. How many snowballs did Maria have?” As students write their solutions, they break apart an addend to make a ten with another addend, and write two equations leading to the solution (see the bond and equations to the right). This movement forward in their ability to record the two steps allows them to own the structure of the ten they have been using for the entire module, on a new level (MP.7). Topic D closes with Lesson 29, where students solve add to with change unknown and take apart/put together with addend unknown problems. Similarly to Lesson 28, students write both equations leading to solution, as they take from the ten (see bond and equation to the right).

## Grade 1 Mathematics Module 2, Topic D

## Downloadable Resources

## Common Core Learning Standards

CCLS | State Standard |
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1.OA.1 | Use addition and subtraction within 20 to solve word problems involving situations of adding to,... |

1.NBT.2.a | 10 can be thought of as a bundle of ten ones — called a “ten.” b. |

1.NBT.2.b | The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight... |