Lesson 7

The purpose of this warm-up is to elicit what students know about length measurement and about units of measurement. While no unit is specified for the ruler in the image, students are likely to bring up centimeters (given the way each 1 unit is partitioned into 10 smaller parts, as seen on centimeter rulers). The work here prepares students to think about the relationship between meters and centimeters later in the lesson.

• Groups of 2
• Display the image.
• “¿Qué observan? ¿Qué se preguntan?” // “What do you notice? What do you wonder?”
• 1 minute: quiet think time

• “Discutan con su compañero lo que pensaron” // “Discuss your thinking with your partner.”
• 1 minute: partner discussion
• Share and record responses.

• Consider sharing that the large insect is a stick insect. (The longest species ever found measured more than 60 cm.) The small insect is a green potato bug.
• “Si cada unidad de la regla mide 1 centímetro, ¿aproximadamente cuánto mide la chinche de papa?” //  “If each unit in the ruler is 1 centimeter, about how long is the potato bug?” (1 cm) “¿Y el insecto palo?” // “What about the stick insect?” (About 16 cm with the antennae, about 12 cm otherwise.)

The purpose of this activity is for students to develop an intuition of 1 meter as 100 times as long as 1 centimeter. Students build a 1-meter long strip out of centimeter grid paper. They use this tool to identify objects or distances that are about 1 meter long.

• Groups of 3–4
• Give each group 2–3 sheets of centimeter grid paper, 2–3 pairs of scissors, and some tape.
• “Cada cuadrado de la cuadrícula de la hoja mide 1 centímetro de largo” // “Each grid on the paper is 1 centimeter long.”
• “En grupo, corten el papel cuadriculado de 1 centímetro en tiras. Después, únanlas para hacer una tira de papel que mida exactamente 1 metro de largo” // “Work with your group to cut the centimeter grid paper into strips and then join them to make a strip of paper that is exactly 1 meter long.”

• “Después de que hayan hecho su tira de 1 metro de largo, identifiquen algunos objetos en el salón de clase o algunas distancias que crean que miden aproximadamente 1 metro de largo. Después, usen su herramienta para comprobar sus predicciones” // “After your 1-meter-long strip is made, identify some objects in the classroom or some distances you think are about 1 meter long. Then, use your tool to check your predictions.”
• 15 minutes: group work on the first two problems
• 2–3 minutes: independent work on the last problem

Students may make a counting error and put together a strip that is shorter or longer than 1 meter. Consider asking:

• “¿Cómo organizaste las partes de 1 centímetro? ¿Cómo las contaste?” // “How did you organize and count the centimeter pieces?”
• “¿Cómo puedes asegurarte de que hay 100 partes de 1 centímetro? ¿Agrupar las partes puede ayudar?” // “How can you make sure there are 100 centimeter pieces? Can grouping the pieces help?”

• Invite groups to share their predictions and the results of their measurement.
• Select students to share their responses to the last problem. If time permits, allow students to measure the arm span or step length of a few students.
• “¿Cuántos cuadrados de la cuadrícula de 1 centímetro unieron para formar 1 metro?” // “How many 1 centimeter grid squares did you put together to make 1 meter?”

In this activity, students analyze student work converting meters to centimeters to develop the understanding that a meter is “100 times as long” as a centimeter. They correct errors in reasoning centering around place value (MP3).

• Groups of 2
• Read the opening paragraph as a class. Ask 1–2 students to reframe the context in their own words.

• “Tómense 5 minutos en silencio para identificar y corregir los errores de Priya y para encontrar la medida que falta. Después, compartan con su compañero cómo pensaron” // “Take 5 quiet minutes to spot and correct Priya’s errors and find the missing measurement. Then, share your thinking with your partner.”
• 5 minutes: independent work time
• 3–4 minutes: partner discussion
• Monitor for students who place zeros for the measurement in centimeters and those who explicitly reason in terms of 100 times the value in meters.

If students place zeros for the measurement in centimeters, ask them to explain their rationale and check if they do so as a result of observing a pattern (for instance, “I noticed that every time we convert from meters to centimeters, the number in centimeters ends in two zeros”) or because they have internalized the value in centimeters as 100 times as much as that in meters.

• See lesson synthesis.