• Quick retrieval from earlier learning (Independent, dependent and control variables; Drawing conclusions from evidence). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Investigation: Does the surface area of a puddle affect how fast it evaporates? Which is the independent variable (the one you change)? (time for the water to evaporate / number of cells / surface area of the water / temperature of the room) → surface area of the waterPrompt: Independent variable: the one you change. Dependent variable: the one you measure.
2. Which conclusion goes too far? Results: cress grew taller with more light, from 0 to 8 hours a day. (Between 0 and 8 hours, more light gave taller cress. / Light affected how tall the cress grew. / Cress with no light grew least. / Cress will keep growing taller with any amount of light, even 24 hours.) → Cress will keep growing taller with any amount of light, even 24 hours.Prompt: The test only went up to 8 hours.
3. Investigation: How does the amount of light affect the growth of cress? Which is the dependent variable (the one you measure)? (height of the cress / amount of light / amount of water / time for one swing) → height of the cressPrompt: Independent variable: the one you change. Dependent variable: the one you measure.

• Show a simple experiment with one thing changed and ask what makes it a fair test.
• Share the objective: Evaluating experiments (research summaries). Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: 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?
• Step 1: In Experiment 2 the different values are given for the mass of the bob.
• Step 2: So the answer is: the mass of the bob
• Answer: the mass of the bob
• 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. 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. In Experiment 2, which variable was changed on purpose? (the acid concentration / the colour of the magnesium / the volume of gas after 1 minute / the temperature) → the temperaturePrompt: Look only at the description of Experiment 2.
2. 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. Which variable was kept constant in Experiment 2 but changed in Experiment 1? (the string length / the time for 10 swings / the mass of the bob / the temperature of the room) → the string lengthPrompt: What was tested in Experiment 1?

• 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. 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 volume of water / the number of seeds that germinated / the temperature) → the volume of waterPrompt: Look only at the description of Experiment 2.
2. 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 increases the dependent variable. / It makes the experiment faster. / It is a control group to compare against. / It is not needed.) → It is a control group to compare against.Prompt: How would you know the fertiliser made a difference?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.