The purpose of this activity is to introduce the inch as a U.S. unit of length. In the Launch, students use inch tiles and classroom objects that are “about an inch” to help them develop a benchmark for an inch. They may continue to use the inch tile to measure lengths in inches or as a tool for checking their measurements with a ruler throughout the lesson.

Although students have measured objects that are not a whole number of units long in previous lessons, it will be more likely that students measure lengths that are clearly not a whole number of inches long. Students should not record measurements to the half inch, but should instead discuss their reasoning to decide which whole number to use and the language they use to express that their measurement is not exactly that number of inches long (MP3, MP6).

• Share a student’s object that is not a whole number of inches long.
• “¿Cómo podemos describir la longitud de _____ cuando su extremo no queda alineado con una de las marcas de pulgada de la regla?” // “How can we describe the length of the _____ when its end doesn’t line up with one of the inch marks on the ruler?” (If it is close to 3 inches, I can write “about 3 inches.”)
• 1 minute: quiet think time
• Share responses.

The purpose of this activity is for students to estimate and measure in inches. Students first estimate the length of given sides of shapes and then measure the sides using inch rulers. In the Activity Synthesis, students share how they measured the different sides and continue to discuss how to communicate the measurement of lengths that are not clearly a whole number of units long (MP6). They also make sure to indicate that their measurements are in inches since students now have both centimeters and inches they can use to measure lengths.

In the Lesson Synthesis, students discuss how they might measure longer lengths in inches. The discussion is designed to elicit their experiences with centimeters and meters and build curiosity for the next lesson in which students measure in feet.

• “Yo observé que algunos estudiantes tenían medidas diferentes del lado más largo del triángulo. ¿Por qué piensan que pasa eso?” // “I noticed that some students had different measurements for the longest side of the triangle. Why do you think that is?” (It was less than 6, but more than 5. It was between 5 and 6 inches.)
• Invite previously identified students to share their reasoning for 6 inches.
• “Algunas veces, el objeto que estemos midiendo tendrá una longitud que esté entre 2 medidas de la regla. Escojan el número que está más cerca del extremo del objeto. Algunas veces, la longitud del objeto en pulgadas puede ser mayor o menor que la longitud real” // “Sometimes, the object we are measuring will have a length that falls between 2 measurements on the ruler. Choose the number that is closest to the end of the object. Sometimes the length of the object in inches may be longer or shorter than the actual length.”