Math lesson plan · 5th grade (Year 6 in England) · 45 minutes
Classify triangles; angles in a triangle
Geometry
CCSS 5.G.B.3CCSS 5.G.B.4CCSS 8.G.A.5England: Y5 GeometryEngland: Y6 Geometry
Objective and success criteria
Students will: Classify triangles; angles in a triangle.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Angles: types and measuring
Leads to: Area of triangles; Pythagoras' theorem; Interior and exterior angles of polygons
Materials: Rulers and protractors, Squared or dotted paper, Shape cut-outs, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Angles: types and measuring). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What type of angle is 90°? (acute / right / obtuse / straight / reflex) → rightPrompt: Compare with a right angle (90°) and a straight line (180°).
- Two angles together make a straight line. One is 139°. What is the other, in degrees? → 41Prompt: Angles on a straight line add up to 180°.
- Three angles meet at a point. Two of them are 48° and 82°. What is the third, in degrees? → 230Prompt: Angles around a point add up to 360°.
Hook · 5 min
- Show a photo of a building, a tile pattern or a road sign and ask what shapes and angles students can spot.
- Share the objective: Classify triangles; angles in a triangle. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A triangle has exactly two sides equal. What type of triangle is it?
- Step 1: It is isosceles.
- Answer: isosceles
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A triangle has all three sides equal. What type of triangle is it? (scalene / isosceles / right-angled / equilateral) → equilateralPrompt: Equilateral: all sides equal. Isosceles: two equal. Scalene: none equal.
- An isosceles triangle has a top angle of 64°. The two base angles are equal. What is one base angle, in degrees? → 58Prompt: The three angles add to 180°.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A triangle has all three sides equal. What type of triangle is it? (right-angled / scalene / isosceles / equilateral) → equilateralPrompt: Equilateral: all sides equal. Isosceles: two equal. Scalene: none equal.
- An isosceles triangle has two equal base angles of 66° each. What is the third angle, in degrees? → 48Prompt: The three angles add to 180°.
Watch out for
- Thinking a square turned on its corner is no longer a square.
- Reading the wrong scale on a protractor.
Support and stretch
Support
- Review first: Angles: types and measuring.
- Use concrete materials: rulers and protractors.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Area of triangles; Pythagoras' theorem; Interior and exterior angles of polygons.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-5.
Free lesson plan from eurekami.com/lesson-plan-builder