Mathematics Support Materials
Mathematics snapshot: Comparing heights
Mathematics/Measurement and Geometry/Using units of measurement
|Relevant aspects of the Achievement Standards
Measure and compare the lengths and capacities of pairs of objects using uniform informal units (ACMMG019)
Students order objects based on lengths and capacities using informal units.
Nature of the assessment
Teacher-devised task and teacher observation
Purpose of the assessment
To check that all students understand that the unit of measure must be the same size when comparing objects.
Stage of the teaching sequence
Start of a series of lessons to check prior understanding.
- The teacher drew an outline of two students, Kai and Emily, who were of similar heights. She glued a piece of paper tape vertically in the middle of each outline to represent the height of each student. She demonstrated measuring the length of Kai's paper tape using paper cut outs of her hand as informal units. She asked the class to count the total number of hands with her and modelled how to use the count to say how many hands tall Kai was. The teacher then recorded the total on the board.
- She repeated this process using large paper clips as informal units to measure the length of Emily's paper tape. She wrote on the board, 'Emily is taller than Kai' and then paused.
- The teacher asked the class, 'Is Emily really taller than Kai? What could I have done wrong?'
- The students then discussed the question in pairs.
The teacher walked around the classroom to identify the students who could or could not explain what she had done wrong. She then led a class discussion specifically choosing students, about whom she had concerns, to answer questions focused on the need for a common unit.
Using the information
Once she was satisfied that most students could explain that the unit of measure must be the same size when comparing objects she moved on to her next teaching point, knowing that she would need to continue to focus some students on the need for a common unit.