Geometry and Spatial Sense, Grades 4 to 6 - EduGains

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Have student pairs read their definitions for the different groups, encouraging them to use
appropriate geometric terminology. Ask other pairs if they sorted their triangles in a similar
manner. Model the appropriate terms (e.g., scalene, isosceles, right), and record terms and
descriptions in an anchor chart for future reference. Alternatively, you might wish to have
students create posters for each type of triangle.
Repeat the process for the sorting of the second property (either angles or side lengths). Ask
questions like the following:
• “Was it difficult to find another way to sort the triangles?”
• “Which property, angles or side lengths, was easier for you to use to find differences in the
triangles? Why?”
• “Can a triangle belong to more than one category?”
• “Did you need to use any tools to help you sort the triangles?”
Note that this last question helps focus in on the properties that are used to categorize triangles – a
ruler measures length, and a protractor measures angles.
ADAPTATIONS/EXTENSIONS
Students who are having difficulty with the task should be encouraged to sort according to
only one property. You might also provide them with a ruler as a hint about how to get started.
This activity is also one in which homogeneous grouping could benefit both struggling students
and those who are able to grasp the concepts quickly. There are many triangles to be sorted,
and a dominant student might quickly move them around, preventing a partner from analysing
them and deciding where they should go.
As an extension, provide students with a copy of 2D5.BLM2: Triangle Sketching Chart. Ask
students to sketch a triangle for each of the nine cells. The triangle must match the characteristics
of both the column header and the row header. Note that it is impossible to draw two
of the triangles (a right equilateral and an obtuse equilateral). This discovery can lead to an
interesting discussion about the measures of angles in a triangle.
ASSESSMENT
Observe students as they solve the problem, and assess how well they:
• identify triangles (i.e., acute, right, obtuse, scalene, isosceles, equilateral);
• classify triangles according to angle and side properties;
• identify and classify two-dimensional shapes by side and angle properties;
• explain sorting criteria and description criteria.
This lesson may be used appropriately to assess students’ use of geometric terminology,
particularly after the Reflecting and Connecting part of the lesson. It is more important that
students use the terms in context rather than recall a definition by rote.
Geometry and Spatial Sense, Grades 4 to 6