• 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 the mass of a bag of flour? (a stopwatch or timer / weighing scales / a measuring jug or cylinder / a thermometer) → weighing scalesPrompt: 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 an ice cube takes to melt / how far a paper plane flew / 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 thermometer / a magnifying glass) → 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. Ben tests whether salt water or tap water freezes faster. Which must he keep the same? (whether the water has salt / the volume of water in each cup / the time each one takes to freeze / the type of water) → 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. Omar tests how the length of a guitar string changes its note. He uses strings of different lengths. What else should stay the same? (the length of the strings / the note he hears / nothing else matters / how tight and thick the strings are) → how tight and thick the strings arePrompt: Tightness and thickness also change the note.
2. Fair tests: which statement is true? (If a result surprises you, you should hide it. / A fair test means everyone gets a turn. / 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.

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