Authentic Lessons for 21st Century Learning

Wild Angles: Acute, and Obtuse, and Right, Oh My!

Geometry and Measurement

Lindsey Link | Published: September 16th, 2020 by Oklahoma Young Scholars/Javits

  • Grade Level Grade Level 3rd, 4th, 5th
  • Subject Subject Mathematics
  • Course Course Elementary Mathematics, Geometry
  • Time Frame Time Frame 1-2 class period(s)
  • Duration More 90 minutes


During this lesson, students will explore and learn about different types of angles. They will practice using a protractor to measure angles and classify angles based on their measurements.

Essential Question(s)

How does geometry help us describe objects all around us?



Students participate in a Card Sort game to classify angle types.


Students collaborate on a Strategy Harvest activity to solve a multiple-step word problem.


Students complete STAR notes to define and illustrate several angle-related terms, and then revisit the Card Sort.


Students identify and label the different angles that are formed by the letters in their names.


Students select an activity to complete from a choice board.


  • Lesson Slides (attached)

  • Card Sort cards (attached; one set per pair of students)

  • Envelopes or paper clips

  • STAR Notes handouts (attached; one per student)

  • Math notebooks (optional)

  • Pencils

  • Paper

  • Protractors

  • Dried spaghetti noodles

  • Mini marshmallows

  • Student tablets with Internet access


Display slide 2. Organize students into pairs, and pass out a set of Card Sort cards to each pair. Give students 10-15 minutes to sort the words, definitions, and examples of different angles.

Display slide 3. Have students move around the room to view how their classmates sorted their cards, looking for any differences.

After students have returned to their seats, have them share out what they noticed about how their classmates sorted the cards. Is there anything they noticed that was different? Similar?

Display slide 4, and share the Essential Question with students: How does geometry help us describe objects all around us?

Display slide 5, and share the learning objectives. By the end of this lesson, students will be able to:

  • Classify and sort shapes based on their angle measurements.

  • Measure the size of angles in various objects.


Display slide 6, and inform students that they are going to explore different ways to solve a problem using a Strategy Harvest. Display slide 7, 8, or 9 to share one of the three multiple-step word problem options described below.

Provide students with time to think about the problem on their own before they begin the Strategy Harvest. Then have them briefly discuss their problem-solving strategies with a series of different partners.

Come back together as a class and have volunteers share out how they would solve the problem. As they are sharing, solve the problem based on their directions. Continue solving until students arrive at the correct answer. Refer to the Exploration Story Problems attachment for notes about various correct and incorrect student responses.


Display slide 10. Pass out copies of the STAR Notes handout, or have students set up a new page in their math notebook. The page should contain three columns, labeled "terms," "definitions," and "examples." In the "terms" column, students should list the following terms, allowing sufficient space for notes after each one: "right angle," "acute angle," "obtuse angle," "straight angle," and "protractor."

Inform students that they will now be watching a music video that contains some important information about angles. Prepare students by telling them that you are going to play the video three times. The first time, they will listen for key information. The second time, they will begin filling in the information on their STAR Notes handout. The third time, they will listen for enjoyment.

Display slide 11 and show the video for the first time, asking students to put down their pencils and listen closely.

Tell students that as they watch for the second time they should raise their hands when they hear information related to one of the terms from their list. Pause the video each time and ask students to share what they heard. Give the class a minute or two to add this information to their notes before resuming the video.

As a class, review your notes. Students should have definitions similar to the following:

  • Right Angle - When an angle measures 90 degrees (slide 12)

  • Acute Angle - Measures between 0 and 90 degrees (slide 13)

  • Obtuse Angle - Measures between 90 and 180 degrees (slide 14)

  • Straight Angle - An angle that is exactly 180 degrees, as in a straight line (slide 15)

  • Protractor - Tool used to measure the degrees of the angle (slide 16)

Have students check their notes and add an image and an example for each term.

Watch the video for a third time so students can just watch and enjoy it. Students can also use this time to fill in any missing information or add to their images or examples.

Display slide 17. Tell students to keep their notes nearby to refer to as they complete the upcoming activities.


Display slide 18. Students will now use their own names to practice using a protractor, measuring angles, and labeling angles. Make sure each student has a blank sheet of paper and a protractor. Ask students to write their names in large capital letters on the paper. Then, students should use their protractors to measure each angle that is formed by the letters. Have students label the angle measurement and the angle type.