### Lesson plan

# The Ten Monster

#### Learning Objectives

Students will be able to calculate ten less than numbers under 20.

#### Introduction

*(5 minutes)*

- Show students a tower of 15 snap cubes.
- Ask, “How many cubes do I have in my tower?”
- Count aloud with students.
- Now ask, “How many cubes would I have if I had 10 less?”
- Have students share a few answers, then take away 10 cubes.
- Count how many are left.

#### Explicit Instruction/Teacher modeling

*(5 minutes)*

- Write on the board 15-10 = 5. Tell students that 15 take away ten is five.
- Point to the number 15 on the number chart. Move your finger to the space directly above 15 (5) and say 15-10=5.
- Remind students that the one in “15” means that the number has one ten.
- When you take away the ten (by subtracting) there are only five ones left.

#### Guided practise

*(10 minutes)*

- Hand out snap cubes to the students. Have them each make a tower of 17 cubes.
- Now tell them that a Ten Monster is coming to town. The Ten Monster loves to eat parts of numbers. He takes one ten from each number.
- Ask students to figure out how many cubes their towers would have if the Ten Monster came and took ten cubes.
- After students solve the problem, have them turn to a partner to share out their answers.
- Have students turn back to the number chart to see that ten less than 17 is 7.

#### Independent working time

*(15 minutes)*

- Pass out Here Comes the Ten Monster! and Ten Less worksheets.
- Have students work independently on the worksheets, circulating around the room to provide assistance as needed.

#### Differentiation

**Enrichment:**Have students create their own “Ten Monster” problems and ask them to trade problems with a partner.

**Support:**Have students complete the worksheets with the help of snap cubes and/or number charts.

#### Assessment

*(5 minutes)*

- Assess students’ understanding by observing how they are subtracting by ten. Are they able to subtract without counting objects one-by-one?
- Assess understanding by looking at students’ completed worksheets.

#### Review and closing

*(5 minutes)*

Have students share some of their answers to the Here Comes the Ten Monster worksheets.