• Quick retrieval from earlier learning (Choosing a measuring tool). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which tool would you use to measure how long a worm is? (a thermometer / a measuring jug or cylinder / a ruler or tape measure / weighing scales) → a ruler or tape measurePrompt: Is it a length, a temperature, a mass, a time or an amount of liquid?
2. What could you measure with a thermometer? (the mass of a pumpkin / the temperature outside / how heavy a pet hamster is / how long a worm is) → the temperature outsidePrompt: What does this tool measure: length, temperature, mass, time or volume?
3. Zara wants to know if her bean plant grows taller each day. What should she use? (a ruler / weighing scales / a stopwatch / a thermometer) → a rulerPrompt: She wants to know how tall it is.

• Show a simple experiment with one thing changed and ask what makes it a fair test.
• Share the objective: Planning a fair test. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Leo tests which paper towel soaks up the most water. What should he change?
• Step 1: He is testing types of paper towel, so that is the only thing he changes.
• Step 2: So the answer is: the type of paper towel
• Answer: the type of paper towel
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Mateo wants to know if plants grow better with more light. Which plan is fair? (Different plants, different water, different light / More water for the plant in the light / Same plant type, same water, different amounts of light / Same light for every plant) → Same plant type, same water, different amounts of lightPrompt: Only the thing being tested should change.
2. Ben tests whether salt water or tap water freezes faster. Which must he keep the same? (the type of water / the time each one takes to freeze / the volume of water in each cup / whether the water has salt) → the volume of water in each cupPrompt: He is changing the type of water and measuring the time.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Which question can be answered with a fair test? (Does a heavier parachute fall faster? / What is your favourite plant? / Who is the best scientist? / Is a rainbow beautiful?) → Does a heavier parachute fall faster?Prompt: A fair test changes one thing and measures another.
2. Fair tests: which statement is true? (A fair test means everyone gets a turn. / You should keep everything else the same. / You should change as many things as possible. / One try is always enough.) → You should keep everything else the same.Prompt: Think about what makes a test fair.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-3.