Triangle Time

Explicit Instruction/Teacher modeling

• Display a T-chart labeled "Triangle" and "Not a Triangle."
• Have students form a triangle with their fingers and repeat after you, "Triangle."
• Show them the images from the Triangle Sort worksheet one at a time. Tell students to give you a thumbs up if the shape is a triangle, and a thumbs down if the shape is not a triangle.
• As students respond whole-group, choose a student to come to the front and tape the shape under the correct category.

Guided Practice

• Reflect with students about how they knew which shapes were triangles.
• Prompt students to notice that triangles have exactly three sides and three corners, the place where two lines meet.
• Have them raise three fingers, and count the sides on one of the triangle examples. Show them an example of a shape that is not a triangle because it does not have three sides and three corners.
• Acknowledge that triangles have straight sides. Have them hold their arm in the air and repeat, "Straight." Have them draw a wavy line with their hand and repeat, "Curved."
• Write "straight" and "curved" on the board with a visual for reference. Show them an example of a shape with three sides that is not a triangle because not all sides are straight.
• Another characterisitc that triangles share is that they are closed shapes. This means that there are no openings in the sides or corners. Have them join their thumbs, but not their pointer fingers to create an open shape with their fingers as they repeat, "Open." Have them join their pointer fingers and repeat, "Closed."
• Tell students that triangles can come in many different sizes and colors, but all triangles have three straight sides, and are closed. Explain that these are the defining attributes, or characteristics, that all triangles have in common.
• Display the Vocabulary Cards, and instruct students to write vocabulary in the Glossary (optional).

Group work time

• Tell students that they will work with their group to build different examples of triangles using straws and pipe cleaners.
• Model the activity by choosing three straws of different lengths. Model bending the pipe cleaner to create corners to join the sides of the triangle. If pipe cleaners are not available, students can build triangles with straws or sticks on paper, draw a dot at each corner, and then connect the dots using a ruler to build different triangles.
• Think aloud about the shape you created. Ask students if it has the defining attributes of a triangle. Say, "Is it closed? Does it have three straight sides?"
• Diplay the sentence frames, "A triangle is ____." and "A triangle has ____." Use the sentence frames to describe the triangle.
• Flip the triangle upside down, and ask students if the shape is still a triangle.
• Challenge students to work together with their groups to create triangles with sides of any length. Prompt students to describe the triangles using the sentence frames.
• Instruct students to break the triangles down and remove the pipe cleaners. Reuse the materials in a lesson about squares and rectangles, or as a center.