Grade 7: Measurement

Warm up with a few quick measurement warm-ups on the board while the class settles, so every child starts thinking about the skill.

The area formulas for triangles (1/2 x base x height) and parallelograms (base x height) both come from the area of a rectangle. This unit covers applying both formulas and finding a missing dimension when the area is already known. Model the method clearly, thinking aloud:

• Show why a parallelogram's area equals base x height by cutting and rearranging it into a rectangle.
• Show why a triangle's area is HALF of base x height by fitting two identical triangles together to make a parallelogram.
• Practise identifying the base and the PERPENDICULAR height in a diagram, since the height is not always a drawn side.
• Solve for a missing base or height by rearranging the formula (dividing the area by the known dimension) once the standard direction is secure.
• Mix triangle and parallelogram problems together so students practise choosing the right formula each time.

Work this through step by step on the board, then have the class talk you through a second one.

• Find the area of a triangle with base 10 and height 6
• 1/2 x 10 x 6 = 30 square units

Do the first few questions of the practice worksheet together, one child explaining each step. Check for understanding before releasing the class to work alone.

Students complete the practice worksheet independently while you circulate and support.

Circulate and look for these, they are the usual sticking points:

• Forgetting to halve the result for a triangle (using the parallelogram formula by mistake).
• Using a slanted side as the height instead of the perpendicular distance from the base.
• Multiplying instead of dividing when finding a missing base or height from a known area.
• Mixing up which dimension is the 'base' when a shape is drawn at an angle.

Pull the class back together. Ask one child to explain measurement in their own words, pose a single check question everyone answers on a mini whiteboard, and name what you will build on next lesson.

Use the independent worksheet as the evidence. A child who can complete it accurately and explain one answer has met the objective; anyone who cannot needs the easier level and a short reteach next session.