2-GM-1-3

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2.GM.1.3 Compose two-dimensional shapes using triangles, squares, hexagons, trapezoids, and rhombi.

In a Nutshell

In first grade, students learned how to compose and decompose larger shapes from/into smaller two-dimensional shapes. Second grade students will continue to combine two-dimensional shapes to create other shapes. For example, a student can use 6 equilateral triangles to build a hexagon. In third grade, students will build three-dimensional figures using unit cubes when a picture or shape is shown.

Student Actions	Teacher Actions
Communicate mathematically by justifying their thinking and explaining two-dimensional shapes according to geometric attributes. Develop accurate and appropriate procedural fluency by sorting shapes into groups with one or more different attributes and justifying their placements. Make conjectures and solve problems about composing shapes while working in groups. Develop the ability to model how to build shapes from other shapes, using diagrams, pattern blocks, geoboards, and tangrams.	Facilitate meaningful mathematical discourse while students describe the attributes of shapes found in the real world. Use and connect mathematical representations by focusing students on the attributes of various shapes, such as a pentagon is a polygon with 5 sides. Elicit and use evidence of students’ thinking as they compare both examples and nonexamples of two- dimensional shapes. Implement tasks that promote reasoning and problem solving in the composition of two-dimensional shapes from smaller shapes.
Key Understandings	Misconceptions
Students can describe attributes of two-dimensional shapes (e.g., number of sides and vertices). Students can compose shapes using materials such as pattern blocks, geoboards or tangram pieces.	The shape changes as orientation changes. An equilateral triangle is the only kind of triangle.