Measuring length centimeters - math grade 2 - lesson 45

Today we are starting something new in math. We are going to begin measurement. Turn to your Shoulder Partner and discuss where in our daily lives we use measurement. What kinds of things do we measure? Why do we measure things? How do we measure things? 

Note to the Teacher: In this lesson, students review what they learned in Primary 1 about measurement.Students measure with standard units of measurement in Primary 2, starting with the centimeter.

STUDENTS DO: Turn to Shoulder Partner and discuss their answers to the teacher’s questions.

TEACHER DO: After about 1 minute, use Calling Sticks to choose 3 or 4 students to share.

STUDENTS DO: Selected students share something their Shoulder Partner said about measurement.

TEACHER SAY: Wow, nice work. We measure a lot of things. We measure how much we weigh, how tall we are, how many liters of water we drink. We also measure time, temperature, and how far we drive. We use different measurement tools for different types of measurement. Today we are going to learn about how to measure length. Say length with me.

STUDENTS DO: Say: length.

TEACHER SAY: LENGTH is the measurement of how long something is from one end to the other end. In Primary 1, you used items like paper clips, crayons, and markers to measure length.

TEACHER DO: If possible, briefly Model this type of measurement for the students using paper clips and a pencil.

TEACHER SAY: You were using non-standard units of measurement. Non-standard means that it is not a measuring tool. Everyone might be using a different kind of tool to measure. Measuring with non-standard tools can be challenging because the tools you use come in different sizes. The pencil may be 3 big paper clips long, but it may be 6 small paper clips long. When we measure using non-standard measuring tools, we can all get different findings for length.

TEACHER DO: If needed, Model another example.

2.TEACHER SAY: This year, we are going to use standard units of measurement. Instead of measuring with objects like paper clips that may be different lengths, we will use a math tool that is the same for everyone. This way, we can all measure the same items and get the same results. The first standard unit of length we will explore is called the centimeter. Say that with me.

STUDENTS DO: Say: centimeter.

TEACHER SAY: A CENTIMETER is a very small unit of measurement. We can use a centimeter to measure small objects like pencils, crayons, erasers, and so on. Hold up your pinky finger in the air.

STUDENTS DO: Hold up their pinky finger in the air.

TEACHER SAY: A centimeter is about the width of the end of your pinky finger. You can see that it is pretty small. It may seem difficult to measure something that small, but there is a tool to help us.

TEACHER DO: Hold up the centimeter ruler.

TEACHER SAY: This is a centimeter ruler. Say that with me.

STUDENTS DO: Say: centimeter ruler.

TEACHER SAY: Centimeter is a long word to write, so we can abbreviate it by writing cm.

TEACHER DO: Write the abbreviation on the board.

TEACHER SAY: Open your student book to page Lesson 45: Apply.

STUDENTS DO: Open the student book to page Lesson 45: Apply.

TEACHER SAY: At the top of the page is a centimeter ruler. Examine the ruler and talk about it with your Shoulder Partner. Talk about what you see and what you think the lines and numbers mean. After 1 minute, I will use Calling Sticks.

TEACHER DO: Allow students about 1 minute to explore the ruler and discuss it with their Shoulder Partner. Then use Calling Sticks to select students to share their observations.

STUDENTS DO: Explore the centimeter ruler with their partner. Selected students share their observations about the ruler.

3.TEACHER SAY: Great observations. Let’s learn how to read a centimeter ruler. Point to the lines and numbers on the ruler.

STUDENTS DO: Point to the lines and numbers on the ruler.

TEACHER SAY: The distance from one long line to the next long line is a centimeter. Put your pinky finger between two lines. Is your pinky finger about a centimeter wide?

STUDENTS DO: Place their pinky fingers between two centimeter lines to help familiarize them with the length.

TEACHER SAY: The numbers on this ruler start with zero and count up. One means 1 centimeter. Two means 2 centimeters, and so on. Let’s count how many centimeters are on our ruler. Point and count aloud with me.

STUDENTS DO: Point to the centimeter lines on the ruler and count them aloud with the teacher

TEACHER SAY: Last year when you measured items, you placed them on the “starting line,” like you do when you start a race. Both items had to start at the same point. It is the same with the centimeter ruler. When we use the centimeter ruler to measure, we have to line up one end of the item we are measuring with the zero line on the ruler. The zero is always the starting line. Point to the zero on your centimeter ruler.

STUDENTS DO: Point to the zero on their ruler.

TEACHER SAY: Let’s practice reading measurements on the centimeter ruler. Look at the first picture. What is it?

STUDENTS DO: Call out: crayon.

TEACHER SAY: Notice that the crayon is lined up to the starting line—zero. To find out how many centimeters long the crayon is, we look at the other end of the crayon. Put your finger on the other end of the crayon.

STUDENTS DO: Put finger on the other end of the crayon.

TEACHER SAY: Give me a Thumbs Up if you know what number is under the end of the crayon.

STUDENTS DO: Give a Thumbs Up if they know what number is under the crayon.Selected students share their answers.

TEACHER SAY: Great job. This crayon is 9 centimeters long. Wave at me if you had 9 centimeters as the answer.

STUDENTS DO: Wave at the teacher if they had the right answer.

TEACHER SAY: Write 9 in the blank under the ruler.

STUDENTS DO: Record the answer under the ruler.

TEACHER SAY: Let’s do one more together. Look at the paper clip and figure out how many centimeters long it is. Give me a Thumbs Up when you have the answer.

STUDENTS DO: Measure the paper clip. Give a Thumbs Up when they are ready. Selected students share their answers.

TEACHER SAY: Wonderful. The paper clip is 4 centimeters long. Wave at me if you had 4 centimeters as the answer.

STUDENTS DO: Wave at the teacher if they had the right answer.

TEACHER SAY: Record the length on the blank under the ruler.

STUDENTS DO: Record the answer.

TEACHER SAY: Do the next three on your own. Be sure to record your answers. When you are finished, compare your answers with your Shoulder Partner. Then we will go over the answers together.

STUDENTS DO: Measure the remaining items on their own. Record their answers. Compare their answers with their Shoulder Partner’s answers.

TEACHER DO: Walk around and observe students as they work and talk to their Shoulder Partner. After all students appear to be finished, go over the answers together. Ask student volunteers to share their answers. Encourage students to correct errors.

STUDENTS DO: Selected students share their answers. Make corrections, if necessary.

TEACHER SAY: You are such great mathematicians. I love how eager you are to learn new things. In our next lesson, we will use centimeter rulers to measure items around the room.Give yourself a pat on the back for your hard work today.

STUDENTS DO: Pat themselves on the back.