• 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: Seeds were kept at 10 °C, 20 °C and 30 °C, all watered daily, and the number that germinated was counted. Experiment 2: Seeds were kept at 20 °C and given 0, 5 or 10 mL of water a day. In Experiment 2, which variable was changed on purpose? (the colour of the pots / the number of seeds that germinated / the temperature / the volume of water) → the volume of waterPrompt: 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 temperature / the volume of gas after 1 minute / the colour of the magnesium / the acid concentration) → the acid concentrationPrompt: What was tested in Experiment 1?
3. Hypothesis: "Plants grow faster in blue light than in red light." Which experiment tests it best? (Plants in blue light only / Identical plants under blue or red lamps of equal brightness, same water and temperature / One plant in blue light outdoors and one in red light indoors / Different species under the same lamp) → Identical plants under blue or red lamps of equal brightness, same water and temperaturePrompt: Only the colour of light should differ.

• 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? (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. What do both scientists agree on? (The water is getting colder. / Low oxygen in the water harms the fish. / Fish numbers have increased. / Fertiliser is the only cause.) → Low oxygen in the water harms the fish.Prompt: 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. A new observation contradicts a well-tested theory. What usually happens? (Science stops / The observation is always thrown away / Scientists check the observation, then improve or replace the theory if it holds up / The theory is never changed) → Scientists check the observation, then improve or replace the theory if it holds upPrompt: Science changes when evidence changes.
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… (Scientist 2 / neither scientist / Scientist 1 / only that fertiliser is harmless) → 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.