Review the previous lesson by having students share their homework
drawings of objects found at home that include triangles. Emphasize
geometry vocabulary such as sides, edges, and angles. Next give the
students brown paper bags that contain objects with distinctive
Have students take turns placing their hands into their bags and
selecting one of the objects to describe (without removing the object
from the bag). Other students pose questions with “yes” or “no” answers
to elicit additional clues from the student holding the shape. After
several cluse have been provided, call on a student to guess the shape.
Discuss with students the vocabulary that helped them identify the
shapes. Their answers should include “sides,” “edges,” “corners,”
“angles,” “triangle,” and so forth. Post these words in the room for
Before distributing geoboards strung with three different-colored
rubber bands, establish rules the class will follow when using them.
For example, geobands are only to be used for constructing shapes on
the geoboards. Give students time to do free exploration with the
geoboards. It may be helpful to demonstrate using an overhead geoboard.
Display triangles and non-triangles, as shown below. Ask students to identify the triangles you have created.
Distribute geoboards strung with three different colors of
rubber bands. Ask students to make triangles using the three different
colors of rubber bands for the sides of their triangles and draw
pictures of them using the same color crayon as the rubber band. (Make
sure the students' concrete and pictorial representations have straight
sides and closed corners.) For drawing the pictures, you may want to
use the Geoboards Activity Sheet.
Geoboards Activity Sheet
Questions for Students
1. How many sides does each triangle have?
2. Please make a triangle that is different from the one you made. Where are other triangles with the same “shape” as yours?
[Student responses may vary.]
3. Would you practice drawing a triangle in the air by watching me draw one in the air?
[Observe students as they follow along with you.]
4. What number do you use most often when you are describing a triangle?
[The number three.]
5. When you draw a triangle without tracing, what do you need to remember?
[A triangle’s sides are straight. A triangle has 3 sides and three corners.]