• 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 much juice is in a carton? (a ruler or tape measure / weighing scales / a measuring jug or cylinder / a thermometer) → a measuring jug or cylinderPrompt: Is it a length, a temperature, a mass, a time or an amount of liquid?
2. What could you measure with a thermometer? (how cold the water in a pond is / how tall a sunflower has grown / how long an ice cube takes to melt / how far a paper plane flew) → how cold the water in a pond isPrompt: What does this tool measure: length, temperature, mass, time or volume?
3. Which is the best tool to find out how long it takes a snail to cross a table? (a ruler / a stopwatch / a thermometer / a rain gauge) → a stopwatchPrompt: "How long it takes" is about time.

• 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. Priya tests which surface a toy car rolls furthest on. What must she keep the same? (nothing / the height of the ramp / how far the car rolls / the type of surface) → the height of the rampPrompt: Only the surface should change.
2. Aisha measures how fast sugar dissolves in water at different temperatures. What does she measure? (the time for the sugar to dissolve / the colour of the sugar / the type of cup / the temperature of the water) → 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. Fair tests: which statement is true? (A fair test means everyone gets a turn. / If a result surprises you, you should hide it. / You should change as many things as possible. / In a fair test you change only one thing.) → In a fair test you change only one thing.Prompt: Think about what makes a test fair.
2. Ben tests whether salt water or tap water freezes faster. Which must he keep the same? (the volume of water in each cup / the type of water / whether the water has salt / the time each one takes to freeze) → 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.