In grade 2, students only measured the length of objects that were whole units and sometimes described lengths as “about 4 inches.” The purpose of this activity is for students to learn that fractions of an inch can be useful for measuring the length of an object that is not exactly a whole number of inches.

Given a ruler marked with inches, students measure objects around the classroom. They may record measurements in whole inches even for objects whose length is not exactly a whole number of inches. In the Activity Synthesis, discuss the need for fractions of an inch to describe lengths more precisely (MP6). 

The rulers from this activity are used in the next activity.

• Display the inch ruler and an object that wasn’t exactly a whole number of inches. (Try to choose at least one object whose length is close to halfway between two whole inches.)
• “¿Cuál es la longitud de este objeto?” // “What is the length of this object?” (between 3 and 4 inches, more than 3 but less than 4, three-and-a-half inches)
• If needed, ask, “¿Podríamos decir que la longitud de este objeto es (un número entero) pulgadas?” // “Could we say that the length of this object is (a whole number of) inches?” (No, It's between 3 inches and 4 inches.)
• “Necesitamos una forma de hacer que nuestras medidas sean más precisas. Vamos a pensar más acerca de esto en la siguiente actividad” // “We need a way to make our measurements more precise. We'll think about this more in the next activity.”

The purpose of this activity is for students to partition the inches on a ruler to show half inches and then use their ruler to measure lengths to the nearest half of an inch.

The unpartitioned rulers from this activity are used in the next lesson.

MLR2 Collect and Display. Circulate to listen for and collect the language and numbers that students use as they measure objects. On a visible display, record numbers, words and phrases, such as “siete mitades de pulgada”, “”, “entre 2 y 3 pulgadas”, “seis y media pulgadas”, “” y “menos de 5 pulgadas” // "seven half inches," "seven halves of an inch," "," "between 2 and 3 inches," "six and a half inches," "," and "less than 5 inches." Invite students to borrow language from the display as needed, and update it throughout the lesson.

• Invite previously selected students to share.
• “¿Cómo midieron la longitud de los objetos cuando la longitud quedaba entre dos marcas consecutivas de su regla?” // “How did you measure the length of objects when the length was in between the marks on your ruler?” (We recorded the mark that was closest. The length was right between 1 inch and inches, so we estimated the length to be about inches.)
• As needed, explain that when measuring to the nearest half inch, the result can be a whole number of inches. For example, if an object's length is closer to 3 inches than to 3 1/2 inches, its length to the nearest half inch is 3 inches (or inches).

• “Guarden ambas reglas (en la que hicieron una partición para mostrar mitades de pulgada y en la que no) para la siguiente lección” // “Save both rulers—the one you partitioned to show halves of an inch and the one that is not partitioned—for the next lesson.”