One Apparatus, Forty-Four Pupils, Thirty-Five Minutes
You teach Grade VIII general science to a class of 44 in a room with fixed benches and no laboratory. For Thursday's 35-minute period the syllabus requires pupils to 'demonstrate that solids expand on heating and contract on cooling' using a ball-and-ring apparatus, and the same practical is examined in the term test in three weeks. You have one apparatus, one Bunsen burner with a slightly leaking collar, a spare gauze and matches. Pupils sit in eight rows of five to six; passing anything down a row takes about 90 seconds. One pupil, Ayesha, has a healed burn on her right forearm and has told you she is frightened of flames. The head has asked that no pupil leave their seat during the period because the corridor is being painted.
1. Write the 35-minute plan with minute-by-minute timings, and state who handles the flame and what the other 43 pupils are doing at each stage.
Read the worked answer
Constraint arithmetic first: 35 minutes, no movement, one apparatus, flame must stay at the front bench, 44 pupils cannot each handle it. Therefore the design is a teacher-operated demonstration with pupil roles at the front and whole-class commitment tasks - not group practical.
| Min | What happens | Who acts |
|---|---|---|
| 0-3 | Ball and ring at room temperature: ball passes through. Every pupil writes a one-line prediction on a slip: 'What will happen after the ball is heated?' | All 44 write; two front-row pupils hold the ring |
| 3-5 | Safety and roles: hair tied, bags under benches, wet cloth and sand bucket placed, rule stated - 'the flame stays on the front bench'. Names the recorder and timekeeper. | Teacher |
| 5-11 | Teacher heats the ball in the blue flame, 60-90 s, turning it. Pupils watch the gap; recorder writes observations on the board. | Teacher holds tongs; pupils observe |
| 11-14 | Ball offered to ring - it will not pass. Two pupils at the front confirm aloud what they saw. | Named pupils speak |
| 14-20 | Ball cooled in water 30 s, re-tested, passes. Second prediction slip collected. | Teacher |
| 20-29 | Explanation with a particle diagram drawn by a pupil on the board; teacher supplies the wording 'the particles move further apart'. | Pupil draws, class choruses the reason |
| 29-33 | Three hand-signal check questions (thumbs up/down) plus a two-item exit ticket. | All 44 |
| 33-35 | Collect exit tickets, dismiss. | Teacher |
Flame: teacher only, always. Pupil helpers hold cold apparatus, time, record - never the burner.
2. Forty-four pupils will watch one demonstration. How will you know whether pupils at the back actually learned the concept rather than merely watched it?
Read the worked answer
Watching is not the risk; passive watching is. Four levers, all cheap:
- Prediction before the event. A written prediction on a slip commits every pupil, including row eight, before the answer is visible. Collect them; a wrong prediction is diagnostic data, not failure.
- Row explainers. Before the demo, appoint one pupil per row as explainer. After the demo, each row has 60 seconds in which the explainer must state the reason ('particles move further apart when heated') while neighbours check it. This puts the explanation through 8 pupils, not 1.
- Board diagram built by a pupil, not drawn by you - a public performance of the model.
- Exit ticket with a transfer item. Question 1: what happened to the ball? Question 2 (transfer): why does a metal lid loosen when you run hot water on it? Sort the 44 into three piles - both correct, recall only, neither. The transfer item, not the recall item, tells you whether the concept travelled.
Follow-up decision rule: if fewer than 30 of 44 get the transfer item, the particle explanation needs re-teaching next lesson before the term test; the demonstration was not the problem.
3. The burner has a leaking collar and Ayesha is frightened of flames. What do you do, and what does your answer show about how you manage practical risk?
Read the worked answer
The leaking collar is the bigger issue and it is not Ayesha's problem. Test-light the burner in the empty room before the class. A collar that leaks allows gas to escape below the flame; in a room with 44 seated pupils and no easy exit you do not light it. If it leaks, switch the heat source: heat the ball in a kettle of just-boiled water poured into a beaker at the front - the ball still expands, the physics is identical, and the risk is scald rather than flame, which is easier to control at a distance.
Ayesha:
- Pre-brief her the day before, privately: what will happen, where the flame will be, that she will not be asked to go near it.
- Seat her near the back with a clear sightline and a clear route out, not in the front row where the flame is closest.
- Give her a genuine role - timekeeper or recorder - so she participates as a scientist, not as an object of concern.
- Never call her forward, never draw attention to her fear, and accept a quiet 'no' without negotiation if she declines even the recorder role.
What this demonstrates: risk assessment precedes enthusiasm. The correct professional sequence is inspect the equipment, remove the hazard, then plan the lesson - not plan the lesson and hope the burner behaves. The demonstration is worth nothing if a pupil is hurt, and it is worth almost as little if one pupil spends it frightened.