• 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 string length / the mass of the bob / the temperature of the room) → the mass of the bobPrompt: Look only at the description of Experiment 2.
2. Experiment 1: A student dropped the same ball from heights of 0.5 m, 1.0 m and 1.5 m onto a wooden floor and measured the bounce height. Experiment 2: The student dropped the same ball from 1.0 m onto wood, carpet and concrete. Which variable was kept constant in Experiment 2 but changed in Experiment 1? (the floor surface / the bounce height / the mass of the ball / the drop height) → the drop heightPrompt: What was tested in Experiment 1?
3. In a drug trial, neither the patients nor the doctors know who gets the real drug. Why? (To stop expectations from biasing the results / Because the drug is secret / To make the trial shorter / To save money) → To stop expectations from biasing the resultsPrompt: People's beliefs can change what they report.

• 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? (Vote on them / Design an experiment where they predict different results / Choose the shorter one / Ignore the data) → Design an experiment where they predict different resultsPrompt: Where do the two ideas disagree?
2. 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? (Neither / Student 2 / Student 1 / Both) → Student 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? (Choose the shorter one / Vote on them / Design an experiment where they predict different results / Ignore the data) → 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. A lake far from any farm also lost fish as it warmed. This supports… (neither scientist / Scientist 1 / only that fertiliser is harmless / Scientist 2) → Scientist 2Prompt: Read each viewpoint and underline its key claim.

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