The purpose of this activity is for students to build any object they want. In the next activity, students focus only on rectangular prisms. As students count, they will need to make sure to count each unit cube once and only once. Monitor for these strategies:

• Touch each unit cube as it is counted.
• Count the unit cubes by layer (including when there are different numbers of unit cubes in each layer).
• Use addition or multiplication when the unit cubes are organized in layers.

• “¿Cómo contaste los cubos unitarios?” // “How did you count the unit cubes?”
• “¿Dónde ves cubos unitarios que se puedan agrupar para contarlos?” // “Where do you see unit cubes that can be counted as a group?”

• Discuss responses to the last problem.
• “¿Cuáles objetos fueron los más difíciles de contar?” // “Which objects were most challenging to count?” (Objects with weird shapes, so I had to count each individual unit cube.)
• “¿Cuáles objetos fueron los más fáciles de contar?” // “Which objects were the simplest to count?” (Organized shapes like towers, rectangles, cubes, or boxes.)
• Invite selected students to share the rectangular prisms they built and how they counted the number of unit cubes.
• “¿Cómo contaron los cubos unitarios?” // “How did you count the unit cubes?” (There were 4 unit cubes in each layer and 2 layers, so that’s 8 unit cubes.)
• “A estos objetos los llamamos prismas rectangulares. ¿De qué maneras contaron los cubos unitarios de los prismas rectangulares?” // “We call these objects rectangular prisms. What were some ways you used to count the unit cubes in rectangular prisms?” (I counted the unit cubes in groups, and then skip-counted. I used multiplication to find the total.)

In the previous activity, students described how to count the number of unit cubes in an object and observed that for a special shape called a “rectangular prism,” the cubes are organized in a structure that makes counting them more systematic. The purpose of this activity is for students to continue to explore rectangular prisms, in particular their structure. As students describe the prisms, they communicate their ideas clearly and precisely (MP6). To describe an object requires students to identify key features of the object and communicate them in an unambiguous way to their partner.

This activity uses MLR2 Collect and Display. Advances: reading, writing.

• Invite partners who built different prisms to share their prisms and descriptions.
• “Sabían cuántos cubos unitarios había en una capa y cuántas capas había. ¿Eso fue suficiente para entender el prisma que su compañero quería que construyeran?” // “Was knowing the number of unit cubes in a layer and the number of layers enough information for you to understand the prism that your partner wanted you to build?” (My partner said there were 6 unit cubes on the bottom and 6 more on top. So I made a row of 6 unit cubes and put another row on top. But my partner had two rows of 3 instead of one row of 6.)
• Use this discussion to update the display, by adding (or removing) language, diagrams, or annotations.
• Invite groups who built the same prisms to share.
• “¿Cómo le describieron su prisma a su compañero?” // “How did you describe your prism to your partner?” (I said how many unit cubes were on the bottom and how tall the prism was.)
• Use this discussion to update the display, by adding (or removing) language, diagrams, or annotations.
• Display any prism made by a student.
• “¿Cómo podemos describir este prisma usando el lenguaje de nuestra presentación?” // “How can we describe this prism, using language from our display?” (Highlight the use of language about “layers” or “stacks.”)