Geometry is my favourite math unit – it relates to the real world, there are all kinds of manipulatives and students tend to enjoy it as well. This is how I like to introduce/review triangles with my grade 8 math students (this could suit any grade, the expectations would just differ):
|Lesson One: Grade 8: Geometry Introduction/Review|
|Minds On (10 mins): Mini Number Talk
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I project it on the board, and I choose the “shapes” category. Then I ask students to think independently about which shape doesn’t belong. After some time, I ask them to share with their group which one doesn’t belong, and that they need to use mathematical reasoning.
Then, as a group they need to agree on which one, and why – then each group will share with the class.
I use some of these questions to prompt discussion:
“Why did you choose that one?”
“Do you agree?”
“Do you disagree? Why?”
“Which answer is the most correct? Is there one?”
|Action (20 mins):
Students should work in pairs
Each pair receives some triangles (I’ve used pattern blocks, paper cut outs, tangrams etc.), a protractor and a ruler.
I ask each pair to categorize their shapes – based on whichever characteristics they’d like – but that they have to have mathematical justifications (not: blue and red etc.)
Once they’ve finished, I ask them to join up with another pair and to justify their sorting, after sharing, they must combine their triangles with that pair and come up with new sorting rules/characteristics.
I leave some discussion prompts on the board:
“Measure all the angles and sides on your triangles”
“Can you classify them in a different way?”
“What do you notice about the sum of all the angles of a triangle?”
|Consolidate/Debrief (10 mins):
I like to bring the students back together to share what they’re thinking, things that they found and the rules they used to classify their shapes. I have groups share their classifications and groupings.
Because this is a formative and introductory activity, I usually circulate throughout to make sure students are on the right track, looking for previous knowledge and misunderstandings etc. I am also looking for their ability to use protractors, think about angles and find relationships between characteristics in triangles.
This is fun, hands-on and the students are doing most of the talking – which makes students and teachers happy!