Lesson Plan

Classifying Triangles by Internal Angles

Classifying figures by features is a fundamental geometry skill. Use this lesson plan to teach your students how to categorize triangles by internal angle types.
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Need extra help for EL students? Try the Describing Angles pre-lesson.
View aligned standards
Need extra help for EL students? Try the Describing Angles pre-lesson.

Learning Objectives

Students will be able to sort triangles based on features of their internal angles.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
EL adjustments


(5 minutes)
Sorting Triangles
  • Start off with a game of Simon Says. Direct your students to imitate you making three different angles with your arms: right angle (one at 90 degrees), an acute angle (one at less than 90 degrees), and an obtuse angle (one greater than 90 degrees).
  • As you make your angle and the students imitate you, tell them the definition of each angle you make. For example, "Simon says make a right angle; this angles is at 90 degrees."


  • Provide visuals of each of the angles with their names for ELs to model.
  • Allow them to repeat the definitions in their home language (L1) or their new language (L2).
  • Define the terms actue angle, obtuse angle and right angle and create hand motions with students' input to represent these terms.


  • Have students restate the definitions using some of the following math key terms: "obtuse," "acute," "right angle," "degrees," etc.