EL Support Lesson

Triangle Time

Students will work hard to build shapes with straws in this hands-on lesson about the defining attributes of triangles. Use alone or with **Know Your Shapes.**
This lesson can be used as a pre-lesson for the Know Your Shapes! lesson plan.
Grade Subject View aligned standards
This lesson can be used as a pre-lesson for the Know Your Shapes! lesson plan.

Students will be able to build triangles that have three straight sides and three corners.


Students will compare and describe different triangles with content-specific vocabulary using sentence frame, visual and peer support.

(5 minutes)
  • Call students to the rug, and instruct them to form a triangle with their fingers by joining pointer fingers and thumbs. Tell them to repeat after you, "Triangle."
  • Ask students to call out other shapes that they know, for example squares, circles and rectangles. Let them know that today they will think about what makes a triangle the same as and different from other shapes.
(5 minutes)
  • 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.
(10 minutes)
  • 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).
(15 minutes)
  • 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.


  • Work in a teacher-led small group to resort the Triangle Sort cards.
  • Groups students at various levels of English-language proficiency together. Group English Learners with supportive peers with more developed English-language skills.


  • Challenge students to build equilateral triangles. Ask them how these triangles are the same as and different from others they have created.
(5 minutes)
  • Circulate as students work to check for understanding. Ask students how they know that these shapes are triangles. Orient the shapes differently by flipping them upside down and sidewides. Check that students are aware that the shapes are still triangles.
  • Invite students to tape an example to a chart titled "Triangles."
(5 minutes)
  • Remind students that they built triangles today. Have students show you on their fingers again how many sides a triangle has.
  • Ask students whether they could build circles with straws and pipe cleaners. Prompt students to realize that this would not be possible because circles have a curved side, and no corners.
  • Ask students if it would be possible to build squares and rectangles with the straws and pipe cleaners. Guide them to recognize that this would be possible because squares and rectangles have straight sides.

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