Bendy ruler
 the validity of the data collected using this investigative method.
 making sure that the method is measuring what will answer the investigative question.
Y6 (03/2010)  Y8 (03/2010)  Y10 (03/2010)  
a) 
i)
ii) 
No The balls are not the same size/might not be the same weight or might be made of different substances. 
moderate very difficult 
moderate very difficult 
very easy very difficult 
NOTE: This resource was trialled at Years 6, 8 and 10. The results showed that the task was difficult for Year 10 students, so is not suitable for Level 3 or 4. However, the data from the earlier levels is included to provide additional diagnostic information to teachers.
•  they are manipulated 
•  they affect the investigation 
•  they interact with each other 
•  their measurements are used to decide the outcome of the test. 
Nature of science: Investigating in science
What to look for Are students able to:

Recognising a fair test
Half of the Year 6 and Year 8 students said this was not a fair test, whereas over 80 percent of the Year 10 students recognised that it was not a fair test. However, when students were asked to explain their reasons for deciding whether the test was fair or not over a third of the younger students and about a fifth of the Year 10 students held the misconception that for an investigation to be fair there needed to be an equal outcome. For example, they said the different bend of the rulers compensated for the different size of the balls. These students have not recognised that fair in science has a technical meaning different from its everyday meaning. The Year 6 students were also more likely to give an explanation that did not make sense or repeated the given information.
Response 
Year 6 
Year 8 
Year 10 
E.g. a large ball needs to be bent more because it is heavy and needs more flick than the smaller lighter ball. 
About a third 
About half 
About a fifth 
Explanation did not make sense or repeated the given information. 
About a quarter 
About 15% 
About 5% 
Recognising the variable
Very few students recognised that the size of the balls was the variable that made the test unfair.
Response 
Year 6 
Year 8 
Year 10 
The balls are not the same size/weight or made of the same substance. 
About 5% 
About 5% 
About a quarter 
Not recognising the independent variable
Some said the bend of the ruler was the variable that made the test unfair. These students failed to see that this was what was being controlled and what the question was about.
Response 
Year 6 
Year 8 
Year 10 
The rulers are bent different amounts. 
About 5% 
About 10% 
About a quarter 
Some students listed both variables.
Response 
Year 6 
Year 8 
Year 10 
The balls are not the same and the rulers need to be bent the same amount. 
About 5% 
About 5% 
About a fifth 
Controls and repeats
A few Year 8 and Year 10 students said it was an unfair test because there was no control. This suggests that they have learnt an aspect of some fair tests, but have not yet learnt when controls are needed. A few also stated that there were no repeats of the tests. This is an important principle for any science tests, not just fair testing.
Good explanations
A good explanation identified the variable that made the test unfair and showed understanding of the independent variable. Two examples from Year 10 students are:
How far she bends the ruler should be the only variable changed. The size of the ball should be kept the same. Annette should use the same type of ball for both flicks. Annette is not measuring what type of ball goes further she is finding out what method of ruler flicking is the most efficient. 
The following explanation is an example of a younger student (Year 6) who has the right idea:
She needs to bend the ruler a lot and flick a small ball. 
This explanation (Year 10) also demonstrates some awareness of the importance of repeating the trials:
She is testing how to bend the ruler to make an object go up as high as it can so she needs to just use one ball and keep using that one only as a constant variable. Also she needs to measure how far she pulls the ruler back and do the same distance a couple of times to make it a fair test. 
They need to ask, "What does the investigation want to find out?" Teachers could scaffold students by asking them to choose between possible answers.
 Will a small ball or a large ball be flicked the highest?
 How does the degree of bend affect the height reached?
Which measurement is used to decide the result?
To decide which measurement is used to determine the result of the investigation students need practise in identifying the dependent variable. They need to ask, "Which variable (measurement) depends on the manipulation of the other variable?" Again in this case the students could choose between:
 the height of the ball (the height of the ball depends on how far the ruler is bent);
 how far the ruler bends (bending the ruler does not depend on how high the ball goes).
Which variable is controlled?
To decide which variable is the independent variable, i.e., the one that is manipulated, students could ask, "What variable is purposely being changed?"
 The height of the ball (the height of the ball is the result of the ruler bending);
 How far the ruler bends (bending the ruler is being manipulated).
Students need to be aware of the reason for using a control  to decide whether a variable is causing a change. To help students, teachers could ask them to decide if all other explanations can be eliminated. If not a control is needed. In contrast, a control is not needed in comparisons where variables are appropriately controlled.
Repeating trials in an investigation.
Students need to know that repeating trials are important in any science investigations (not just a fair test) to ensure reliability of the data. This occurs because by repeating trials:
 any rogue result can be easily seen and allows the student to explore possible reasons for the error;
 averaging trial results gives a more accurate measurement.