Geometry and Spatial Sense, Grades 4 to 6 - EduGains

GETTING STARTED
Place a picture of a triangle on the board or an overhead projector. Invite students to share
what they observe about the triangle with an elbow partner. Open the discussion to the larger
group. Record the students’ observations on the board as they share their discussions. Place
a second (different) triangle beside the first and ask students to share their observations of
this triangle with an elbow partner. Open the discussion to the larger group and record their
observations. Invite students to compare and contrast the two triangles. Explain to students
that in this lesson they will be working with a partner to examine and sort a variety of triangles.
WORKING ON IT
Students will work with a partner for this activity. Provide each pair of students with a copy of
2D5.BLM1: Assorted Triangles and scissors with which to cut out the triangles on the blackline
master. Explain to students that their task is to sort the entire collection of triangles into three
groups so that no triangle belongs to two groups. When they have sorted the triangles, they must
record a name for each group, as well as a description that defines the group of triangles.
When students have created their groups and developed a definition for each, encourage them
to repeat the activity but to use a different sorting criterion. Again, students should name each
group and write a description that defines the group.
As students work, observe how they discuss the properties of the triangles. Do they notice angles,
and if so, how do they describe the angles? Do they notice congruent sides? What kind of language
do they use for recording the descriptions of the groupings? If a student pair is stuck on only
one property (e.g., side length), you may have to hint at the other property (e.g., angle measure).
However, it is best if students struggle somewhat with the activity before you provide them with
hints. Look for student pairs to share their findings during the reflection part of the lesson.
REFLECTING AND CONNECTING
Bring the students back to the larger group. Ask various pairs to share one of the ways in which
they sorted the triangles (either angles measures or side lengths). You may have a student pair
read out the triangle letters in a grouping, and then you may challenge the class to look at the
triangles in that grouping and predict the description before the pair shares it. Ask the class
questions like the following:
• “Which types of triangles did you look for first?”
• “What was the first thing you noticed about some of the triangles?”
• “When you found all the triangles for one group, how did you decide what the next group
would be?”
Grade 5 Learning Activity: Two-Dimensional Shapes – Triangle Sort 1 1