Area of shapes
| Y4 (10/2010) | ||
| a) |
Draws 8 unit squares. - Give credit for students who use other drawings with an area of 8 square cm. - Do NOT accept responses where several disconnected shapes are drawn. - Do NOT give credit if squares of different sizes are drawn. easy |
easy |
| b) |
Draws 17 unit squares. - Give credit for students who use other drawings with an area of 17 square cm. - Do NOT accept responses where several disconnected shapes are drawn. - Do NOT give credit if squares of different sizes are drawn. moderate |
moderate |
| c) |
B Any 1 of the following:
Look for visual clues, such as marks around the perimeter, or dots in the boxes as they were counted. B and correct explanation |
easy difficult difficult |
This resource looks at students' ability to use unit squares as measure of area. They do this firstly by constructing areas of given sizes, and then chose and justify which of two shapes has the biggest area. There is the potential for multiplicative strategies, either multiplying rows by columns or repeated addition/skip counting.
| Likely reason | ||
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a) b) |
7 or 9 16 or 18 |
Miscounts the squares These students drew one square too few or too many. |
| c) |
Uses only width (length) or height B - Because longer is bigger than fatter. A - Fatter is bigger. B – Because if you turn it, it will be taller. And if you leave it, it will be wider. B – Because it is wider than A. |
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| c) |
Sees area as a property of the shape A – [A] square is bigger than a rectangle. B – Because … rectangles are bigger than squares. |
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| c) |
Confuses area and perimeter B – Because you count how many squares are next to it. B - It has a wide space around it. B – Because I counted the little boxes around it and B was the biggest number. Look for visual clues, such as marks around the perimeter. |
Miscounts the squares
Get the student to confirm their answer. If they can see that it is incorrect, then they are probably achieving at curriculum level 1, but need to learn to work more carefully and to check their work after it is completed.
If their answer is one square too few in a) and b), ask them to justify it. If they say "There already is one square there" they are probably achieving at curriculum level 2.
Uses only width (length) or height or sees area as a property of the shape
These students may well be estimating the area visually, which is a Level 1 approach. They need to move on to measuring the area by counting unit squares. Their ideas could be challenged by drawing a 3 × 3 square and a 1 × 8 or 1 × 10 rectangle and asked "Which is bigger?" A discussion could lead to the conclusion that they would have to count the unit squares to be sure.
Confuses area and perimeter
The meaning of the words "perimeter" and "area" is a knowledge issue. Students need to see both concepts are valid measures, but they measure different things.
- Perimeter measures the length of the distance around. This can be counted using unit lengths (counting from one on materials), or by adding the lengths of each side.
- Area measures the "space" covered on a flat surface. Analogues such as "How much paint is needed?" or "Which one will take longer to colour in?" may be useful.
Part c) asks for the bigger shape. This implies the biggest size of the shape, and size of a flat shape is measured in area. You could say to the student "You have given the shape which has the bigger distance around it. This is called the perimeter. Can you tell me which shape has the bigger area?"