Look at these two bags: one paper, one plastic. If heavy rain started on the way home from school, which bag would keep your books dry, and how could we find out without just guessing?
Hold up a clean paper bag and a clean plastic bag (or two photos on the IWB if bags are scarce). Take three or four quick ideas only. Do not name the four test properties yet and do not hand out materials.
Key question: How could we test our ideas fairly instead of arguing?
Nature of STEM cue: engineers and materials scientists choose materials by testing properties against the job, not by guessing what looks strongest.
Those bags look different because their materials have different properties: things we can test about them.
Property: something true about a material that we can test.
Waterproof: water does not soak through, so the other side stays dry.
Strong: resists tearing or breaking when pulled.
Flexible: bends or folds without snapping or cracking.
Transparent: you can see clearly through it when you hold it up to the light.
Which property would matter most for a raincoat, which for a window, and which for a carrier bag that must hold heavy books?
| Concept | Why it matters | Example |
|---|---|---|
| Property — something true about a material that we can test | Jobs fail when we pick a material for looks alone; properties tell us what it can actually do | A shopping bag needs strength more than prettiness if it is to carry heavy books home |
| Waterproof — water does not soak through, so the other side stays dry | Irish weather is often wet, so covers, coats and outdoor bags need this property | Five drops of water sit on plastic; the underside stays dry |
| Strength — how well a material resists tearing or breaking when pulled or loaded | Weak materials rip under weight and spill what they carry | Foil tears with a firm pull; thick card holds longer |
| Flexible — bends or folds without snapping | Some jobs need folding (a screen, a bag that packs away); others need stiffness | Fabric folds flat; stiff card creases and may crack |
| Transparent — you can see clearly through it when held to the light | Windows, covers for growing plants, and viewing panels need light or sight through them | Clear plastic shows the print underneath; foil blocks it completely |
Misconception to head off: thicker does not always mean better. Thick card can be strong yet useless for a window because it is not transparent, and foil can feel tough yet tear under a pull.
Worked model (say this aloud before groups test): I wonder whether this foil is waterproof. I predict the water will sit on top because cooking foil keeps food juices in. I place five drops on a 10 cm square, wait thirty seconds, and check the underside on dry paper. I observed the drops stayed on top and the paper under the foil stayed dry, so I think foil is waterproof for this short test. Model only waterproofness on foil; leave strength, flexibility and transparency for the class.
Also name opaque briefly if a child asks: you cannot see through it at all. Keep the board words to property plus the four test words above.
Our question: which of our four materials is best for different everyday jobs?
Look at fabric, plastic, foil and card. Share with your partner:
Which material do you predict will keep water out, and why?
Which will let you read a word through it, and why?
We will check strong and flexible carefully when we test, using the same rules for every sample.
Before this step
Have four labelled sample trays ready (fabric, plastic sheet or bag, aluminium foil, card), cut to roughly the same size so comparisons stay fair. One water tray, dropper or teaspoon, dry underside-check paper, and each pupil's Investigation Journal page to hand.
Discussion shape
Whole class, then 30-second partner talk. Predictions are never wrong; they start the science. Keep this beat to the two focus predictions on the board (waterproof and transparent) so the talk stays light.
- Ask: Which material do you think will keep water out?
- Ask: Which will let us read a word through it?
Capture two or three predictions on the board without ranking them as correct. If a child volunteers a strength or flexibility idea, note it briefly and say you will test those with a shared rule next.
Fairness cue (light, not a full fair-test lesson yet): same size pieces, same number of water drops, same gentle pull for a count of three. Full fair-test planning comes later in this unit.
Work as a group. Test one property at a time across all four materials before moving on. Tick pass or fail on your Investigation Journal page as you go so you do not have to remember everything.
Waterproof: place five drops of water on the sample, wait thirty seconds, lift it and check the underside on dry paper (dry = pass).
Strong: two people hold opposite edges and pull gently while the group counts to three. Pass = it does not tear or start to rip. Fail = it tears or rips.
Flexible: fold it double; pass = it bends without cracking.
Transparent: hold it over a printed word; pass = you can read the word clearly.
Talk as you go: one thing you noticed for each test.
Setup
Groups of three or four. Each group gets one set of four same-size samples, a shallow tray, water in a jug or cup, a dropper or teaspoon, a scrap of printed paper for the transparency test, a dry paper towel or scrap sheet for the waterproof underside check, and each pupil's Investigation Journal page to record on directly.
Recording: pupils record pass or fail straight onto their Investigation Journal page as they test each material, in the 'Our comparison' table. They head the empty columns with the four properties (waterproof, strong, flexible, transparent) and list the four materials down the 'What we tested' column. Nothing is written on a separate card and nothing is copied across later.
How to run it
Remind them of the foil waterproof model. Circulate and ask: What did you observe, not what did you hope? If a group rushes, slow them to one property at a time across all four materials, ticking each result on the journal page before the next property.
Shared strength rule (say it once to the class): two holders, gentle pull only, count to three together. Pass means no tear and no start of a rip. This keeps group results comparable.
What good testing looks like: same drop count, samples flat on the tray, underside checked on dry paper, shared pull rule, honest pass/fail ticks on the journal page before moving on.
If results disagree between groups: that is useful. Ask whether sample thickness or how hard they pulled changed the outcome. Note it for the make-sense step.
Differentiation: less confident groups complete waterproof and transparent first (clearest results). Confident groups add a second strength check (can it hold two exercise books without tearing when used as a sling) and note it on the journal page.
Safety: water on floors is a slip risk; no tasting materials; foil edges can be sharp if torn.
Your Investigation Journal page now shows a pass or fail for each material (fabric, plastic, foil and card) across all four tests: waterproof, strong, flexible and transparent.
Read across your comparison table and talk with your group. Which material passed the most tests? Which failed a test you thought it would pass?
On your journal page, write one short note for anything surprising (for example, a material that felt strong but tore, or one that looked clear but was hard to read through). Then write one sentence saying which material you think is best for keeping things dry, and why.
This is the in-lesson make-sense beat. The pass/fail results are already on the Investigation Journal page from Step 4, so there is nothing to copy across. Use this time to read the comparison table and draw first conclusions before recommendations.
Look-fors:
- Every material has a result for each property (no blanks) already ticked from testing.
- Pupils read across their own table, not from the earlier prediction.
- At least one honest surprise note from most pupils, plus a first evidence-based sentence about the best material for keeping things dry.
If a pair finishes early, they re-check one disputed result on the samples rather than starting a new investigation on devices.
Typical pattern many classes find: plastic often waterproof and flexible; foil waterproof but tears and is not transparent; card stronger and stiffer, not waterproof; fabric flexible, often not waterproof unless coated.
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