Year 7 Science · Unit 2 · Lesson 19

Working Scientifically — Fair Tests

Challenge Worksheet

Name

Date

Class

Learning Goals

Evaluate a student's investigation report and identify flaws that reduce validity or reliability.
Distinguish between problems with the method (validity) and problems with the results (reliability).
Propose specific improvements to make an investigation more scientifically rigorous.

Go Deeper

Evaluate the investigation report

A student wrote this investigation report

"I wanted to find out if the type of sugar affects how quickly it dissolves. I used icing sugar, raw sugar and white sugar. I added a spoonful of each to a cup of water and timed how long it took to dissolve. I used hot water for the icing sugar because it takes longer, and cold water for the other two. I only tested each sugar once because I ran out of time. I concluded that icing sugar dissolves fastest because particles in powder form are more exposed. My experiment was a fair test because I used the same cup each time."

(a) Identify three specific flaws in the student's method. For each flaw, state whether it reduces validity or reliability.

Challenge 3 marks

(b) The student claims: "My experiment was a fair test because I used the same cup each time." What is wrong with this reasoning? What does a fair test actually require?

Challenge 2 marks

Show What You Know

1. The student concluded that "icing sugar dissolves fastest because particles in powder form are more exposed." Is this conclusion supported by the investigation as described? Explain your reasoning using the concepts of validity and controlled variables.

Challenge 3 marks

2. Rewrite the method for this investigation so that it is both valid and reliable. Include: what the IV, DV and controlled variables would be, how many trials you would run, and one specific safety precaution.

Challenge 4 marks

Wrap Up

In one sentence, what was the main idea of this lesson?