We know that squares are special types of rectangles from 2nd grade. Now were extending the idea of subsets much further, although we don’t use the word “subset” when talking to 3rd graders. In this section, students will learn that quadrilaterals include squares, rectangles, rhombuses, and trapezoids. Squares are special rhombuses as well as rectangles. They will also learn how to draw shapes that are none of these things. For example, any quadrilateral that is concave. Again, we don’t say “concave,” we just reason that it cannot be a rectangle, rhombus, or trapezoid because it doesn’t have a right angle, doesn’t have four sides of equal length (equilateral), and doesn’t have a pair of parallel sides.

Intro to quadrilaterals by Khan Academy

Do these Khan Academy exercises:

Next, give your students these challenges:

- One Million to Seven by NRICH
- En-counters by NRICH

Conclude by leading this investigation:

Place Value

by MathPickle

3.G.A.1: Understand that shapes in different categories (e.g., rhombuses, rectangles, and others) may share attributes (e.g., having four sides), and that the shared attributes can define a larger category (e.g., quadrilaterals). Recognize rhombuses, rectangles, and squares as examples of quadrilaterals, and draw examples of quadrilaterals that do not belong to any of these subcategories.