Lesson objective: Understand that a circle is the set of points that are all the same distance from another point, called the center.

Students bring prior knowledge of circles from grade 3 (3.G.A1) and grade 4 (4.MDA.3). This prior knowledge is extended to circles as students discover what a circle actually is. A conceptual challenge students may encounter is defining what a circle is using only straight lines and points.

The concept is developed through work with straight lines (such as toothpicks) and points (such as marshmallows), which will be used to represent radii and points, respectively.

This work helps students deepen their understanding of equivalence because although circles are different from other two dimensional shapes, they still have a perimeter (circumference) and area.

Students engage in Mathematical Practice #1 (Make sense of problems and perservere in solving them) as they manipulate the straight lines and points to represent a circle.

**Key vocabulary:**

**Special materials needed:**

- toothpicks and mini-marshmallows (not required but helpful for students)