• 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 warm the classroom is? (a thermometer / weighing scales / a stopwatch or timer / a ruler or tape measure) → a thermometerPrompt: Is it a length, a temperature, a mass, a time or an amount of liquid?
2. What could you measure with a stopwatch or timer? (the mass of a bag of flour / how cold the water in a pond is / how long it takes to run 50 metres / the width of a leaf) → how long it takes to run 50 metresPrompt: 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 magnifying glass / a ruler / a thermometer / a measuring jug) → 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. Why is it a good idea to repeat a test several times? (Because the first try never counts / To make the test unfair / To check the results are reliable / To change the answer) → To check the results are reliablePrompt: What if one result was a mistake?
2. Aisha measures how fast sugar dissolves in water at different temperatures. What does she measure? (the type of cup / the colour of the sugar / the temperature of the water / the time for the sugar to dissolve) → the time for the sugar to dissolvePrompt: She changes the temperature. What does she then look at?

• 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. Priya tests which surface a toy car rolls furthest on. What must she keep the same? (the height of the ramp / how far the car rolls / nothing / the type of surface) → the height of the rampPrompt: Only the surface should change.
2. Ben tests whether salt water or tap water freezes faster. Which must he keep the same? (the time each one takes to freeze / the volume of water in each cup / whether the water has salt / the type of water) → the volume of water in each cupPrompt: He is changing the type of water and measuring the time.

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