Guided Lessons

# 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.
Need extra help for EL students? Try theDescribing AnglesPre-lesson.

No standards associated with this content.

No standards associated with this content.

No standards associated with this content.

No standards associated with this content.

No standards associated with this content.

Which set of standards are you looking for?

Need extra help for EL students? Try theDescribing AnglesPre-lesson.

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.
(5 minutes)
• 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."
(10 minutes)
• Hand out and preview the Sorting Triangles worksheet and observe the shape labeled #9 in the shapes box.
• Have students review the angle categories, turn to a neighbour and share which category triangle #9 belongs in.
• Allow for students to determine that it is an obtuse triangle and place the number 9 on the proper section of the diagram where obtuse does not overlap with another category. Answer any clarifying questions.
(5 minutes)
• Repeat the process for another shape, but allow students to determine the proper placement of the shape number.
(15 minutes)
• Have your students complete the remaining exercise on the Sorting Triangles worksheet.

Support:

• Inform students to cross off items that don't qualify for categorization (e.g., the quadrilaterals) to limit potential triangle choices.
• Students can focus on one angle type at a time (e.g., acute triangles) and cross off their choices as they go.

Enrichment:

• Students can make a poster for one or both of the Thinking Deeper activities using pictures, words, and numbers.
(5 minutes)
• Show students three different types of triangles numbered 1, 2, and 3. Say a category (i.e., obtuse triangle, acute triangle, right triangle) and have them show a number with their fingers for the category the triangle belongs to.
• Choose students to share their rationale using some of the key terms from the lesson.
(10 minutes)
• Review the answers as a class and allow for peers to assist with incorrect responses.
• Assign an exit ticket activity where students modify one of their choice of angles 6–8 so that they COULD be placed in one of the three diagram categories.