A critical area of instruction in third grade is for students to describe and analyze two-dimensional shapes. Students compare common geometric shapes (e.g., rectangles and quadrilaterals) based on common attributes, such as four sides (3.G.1).
In earlier grades, students informally reasoned about particular shapes through sorting and classifying based on geometric attributes. Students also built and drew shapes given the number of faces, number of angles, and number of sides.
In third grade, students describe properties of two-dimensional shapes in more precise ways, referring to properties that are shared rather than the appearance of individual shapes. For example, students could start by identifying shapes with right angles, explain and discuss why the remaining shapes do not fit this category, and determine common characteristics of the remaining shapes.
In third grade, students continue to relate shapes and fractions, recognizing that the shape must be partitioned into equal-size pieces in order to represent a fraction of the shape. For example:
This circle is divided into four equal-size pieces and each piece is one-fourth of the circle.
This circle is not divided into four equal-size pieces and each piece is not one-fourth of the circle.