• Quick retrieval from earlier learning (Evaluating experiments (research summaries)). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Experiment 1: A pendulum with a 0.5 kg bob was timed for 10 swings with string lengths of 0.25 m, 0.50 m and 1.00 m. Experiment 2: A 1.00 m pendulum was timed with bobs of 0.1 kg, 0.5 kg and 1.0 kg. In Experiment 2, which variable was changed on purpose? (the time for 10 swings / the temperature of the room / the mass of the bob / the string length) → the mass of the bobPrompt: Look only at the description of Experiment 2.
2. Experiment 1: Magnesium ribbon was added to hydrochloric acid at concentrations of 0.5, 1.0 and 2.0 mol/dm³ at 25 °C, and the gas volume after 1 minute was measured. Experiment 2: The 1.0 mol/dm³ acid was used at 15 °C, 25 °C and 35 °C. Which variable was kept constant in Experiment 2 but changed in Experiment 1? (the colour of the magnesium / the volume of gas after 1 minute / the acid concentration / the temperature) → the acid concentrationPrompt: What was tested in Experiment 1?
3. A scientist tests a new fertiliser on 20 tomato plants. Another 20 plants get no fertiliser. What is the purpose of the second group? (It makes the experiment faster. / It is not needed. / It increases the dependent variable. / It is a control group to compare against.) → It is a control group to compare against.Prompt: How would you know the fertiliser made a difference?

• Show a simple experiment with one thing changed and ask what makes it a fair test.
• Share the objective: Comparing scientific explanations (conflicting viewpoints). Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Two students explain why a ball rolling on a flat floor eventually stops. Student 1: Objects naturally slow down and stop when nothing keeps pushing them. Student 2: Friction and air resistance act against the motion; with no resistive forces, the ball would keep moving at a steady speed. Which student's view agrees with Newton's first law?
• Step 1: Newton's first law: an object keeps moving at constant velocity unless a resultant force acts.
• Step 2: So the answer is: Student 2
• Answer: Student 2
• 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. Two hypotheses explain the same data. How can scientists decide between them? (Design an experiment where they predict different results / Vote on them / Ignore the data / Choose the shorter one) → Design an experiment where they predict different resultsPrompt: Where do the two ideas disagree?
2. Two scientists explain why the Moon shows phases. Scientist 1: Earth's shadow covers different amounts of the Moon during the month. Scientist 2: Half of the Moon is always lit by the Sun; as the Moon orbits Earth, we see different amounts of the lit half. Which scientist's explanation is accepted by astronomers today? (neither / Scientist 2 / Scientist 1 / both) → Scientist 2Prompt: Read each viewpoint and underline its key claim.

• 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 6 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. Two hypotheses explain the same data. How can scientists decide between them? (Vote on them / Design an experiment where they predict different results / Ignore the data / Choose the shorter one) → Design an experiment where they predict different resultsPrompt: Where do the two ideas disagree?
2. Two scientists explain why some lakes have fewer fish than ten years ago. Scientist 1: Farm fertiliser washed into the lakes caused algae to grow; when the algae died, bacteria used up the oxygen in the water. Scientist 2: Warmer water from climate change holds less dissolved oxygen, so fewer fish survive. What do both scientists agree on? (Fertiliser is the only cause. / The water is getting colder. / Fish numbers have increased. / Low oxygen in the water harms the fish.) → Low oxygen in the water harms the fish.Prompt: Read each viewpoint and underline its key claim.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.