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 geometric properties.
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 future reference.
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.
