Year 8 Science · Unit 4 · Lesson 3

Variables — IV, DV and Controlled

Challenge Worksheet

Name

Date

Class

Learning Goals

Identify IV, DV, and controlled variables across multiple research questions.
Evaluate a flawed investigation and identify multiple confounding variables.
Redesign an invalid investigation into a fair, controlled experiment.

Warm Up

Design — identify variables

For each research question, identify the independent variable (IV), dependent variable (DV), and three controlled variables in the table below.

Research question	Independent variable	Dependent variable	Three controlled variables
Does surface type affect how far a toy car rolls?
Does exercise intensity affect recovery heart rate?
Does soil type affect seed germination speed?

Go Deeper

Evaluate the claim

A student claims...

"I proved that caffeine improves exam performance. Five of my friends all drank coffee before their maths exam last Tuesday and every one of them scored above the class average. That's clear scientific proof that caffeine works."

(a) Identify the independent variable and dependent variable the student appears to be investigating.

Challenge 2 marks

(b) Identify at least three confounding variables in this "investigation" that could explain the result without caffeine having any effect.

Challenge 3 marks

(c) Explain why this investigation cannot be used as scientific evidence, even though all five friends scored above average. Use the terms "fair test," "controlled variables," and "validity" in your answer.

Challenge 3 marks

(d) Describe how you would redesign this investigation to produce valid data. Include the IV, DV, at least three controlled variables, and a comparison group.

Challenge 4 marks

Wrap Up

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