• 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 candle burns? (a thermometer / a stopwatch or timer / a measuring jug or cylinder / weighing scales) → a stopwatch or timerPrompt: Is it a length, a temperature, a mass, a time or an amount of liquid?
2. What could you measure with a measuring jug or cylinder? (how long it takes to run 50 metres / how heavy an apple is / how much rainwater was collected / how heavy a pet hamster is) → how much rainwater was collectedPrompt: What does this tool measure: length, temperature, mass, time or volume?
3. Which tool would show that the water in a bowl is getting colder? (a measuring jug / a ruler / a magnifying glass / a thermometer) → a thermometerPrompt: Colder means the temperature is going down.

• 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. Leo tests which paper towel soaks up the most water. What should he change? (the time he waits / the type of paper towel / the amount of water / the size of the towel) → the type of paper towelPrompt: In a fair test you change only one thing: the thing you are testing.
2. Ben tests whether salt water or tap water freezes faster. Which must he keep the same? (the time each one takes to freeze / whether the water has salt / the type of water / the volume of water in each cup) → 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. Mateo wants to know if plants grow better with more light. Which plan is fair? (More water for the plant in the light / Same light for every plant / Same plant type, same water, different amounts of light / Different plants, different water, different light) → Same plant type, same water, different amounts of lightPrompt: Only the thing being tested should change.
2. Fair tests: which statement is true? (If a result surprises you, you should hide it. / One try is always enough. / You should change as many things as possible. / Repeating a test helps you check your results.) → Repeating a test helps you check your results.Prompt: Think about what makes a test fair.

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