This is a quick and fun group activity to introduce your class to different types of triangles.

Materials needed:

- Construction paper (one sheet per student and a different color per student so each student at a table has a different color)
- Scissors and pencils
- Rulers and optional protractors

Have each student draw as many different triangles on their paper. Tell them that the types should not be by size, like small, medium, and large. Each triangle should be around the size of the palm of their hand and they should figure out how to use most if not all of their paper.

After everyone has cut out their triangles. Tell them to sort them together with their table mates. Most will start sorting by color. When this happens I will say, “Hey you sorted like this when you were younger, see if you can come up with another way to sort them.”

When they have sorted them, have them arrange them neatly on their table and then do a “Museum Walk.” I remind them that at a museum, they whisper or are silent and wander around and look at all the different tables and wonder how they sorted the triangles. They shouldn’t talk to each other.

After the Museum Walk, you can have each group share how they sorted them, or you can have students ask other tables how they sorted them. Some tables will be obvious, others will need to be asked. Then do another round, and they need to sort them another way. In my experience, most will sort by lengths of sides first and then angles. They will use terms like straight corners, long and skinny sides, matching sides, etc. It’s so fun.

After take a sample of triangles from a group, and ask them what they would call this group, they will use words like “long and skinny” “all the same” “big angles” etc. You can then say that these are actually called “isosceles” “equilateral” “obtuse” etc. Have them show you the different triangles as you describe them and write the terms and definitions. See if they understand that a triangle can be characterized by the length of the sides (scalene, isosceles, equilateral) as well as the angles (obtuse, acute, right, and equilangular), so triangles will have both descriptions. As you describe the triangles have them sort those out, see if there are an triangles left. They will be amazed that the created such a variety of triangles at the beginning, but that they all can be described in a couple of terms.

Some follow up ideas:

- Use the different triangles to make brochures and posters
- Glue them into their math journals or dictionaries
- Make a triangle game by gluing triangles to index cards and then write the triangle name (both by lengths and/or sides) onto another index card for a quick match game

Thanks for reading and let’s make math magic!

– Evil Math Wizard