Hold up one ice cube, one plain chocolate square and a small lump of butter so the whole class can see them. Keep the warm-water set-up out of sight for now so the hook stays a curiosity beat, not the full set-up.

Take three quick hand counts (ice, chocolate, butter) and leave the guesses on the board as tally marks. Do not correct anyone yet. Predictions are the start of the science.

Before the lesson: freeze same-size ice cubes; break plain chocolate into equal squares; cut small equal lumps of butter; set a jug of warm (hand-safe, not hot) water ready but keep it off the pupil tables. Print the Investigation Journal page.

Keep this board light: only melt and cool before the demo. Hold the full idea of reversible change until after the cooling watch (step 5), when pupils have seen something firm up or heard why water needs a freezer.

Use the table below as your own reference while you talk.

Misconception to head off later (not yet): children may say melted chocolate has "gone" or been destroyed. It is still chocolate, only in liquid form. Also, "reversible" does not mean it always happens by itself in the classroom: ice water needs a freezer (or a very cold place) to become solid ice again.

Nature of STEM: cooks and chefs have always used gentle heating and cooling: melting butter for baking, setting chocolate, freezing water for ice. People worked these changes out by watching carefully long before science lessons named them.

Agree the question together on the board. Predictions are never wrong; they are the start of the science.

Circulate while pupils record a quick prediction for each material. Sentence stems if needed: I think the ice will… because… / I think the chocolate will… / I think when we cool them…

Invite three volunteers to share one prediction aloud. Keep the class folded in: Do you agree? What would you add?

Differentiation: some pupils may draw symbols (solid block → puddle) instead of full sentences. That is fine if they can say their idea aloud.

Before you start

Set up so the materials list alone is enough: pour warm, hand-safe water into the basin or large roasting tin. Place the three identical small foil dishes on the shallow tray or baking sheet. Rest that tray in the basin so the underside of the tray is in contact with the warm water, while the dishes stay dry inside the tray. Do not try to float the loaded tray. Put one same-size ice cube, one plain chocolate square and one small lump of butter each in its own dish. Pupils stand back in a viewing arc with pencils ready. No pupil pours water or handles the tray.

Pencils during the watch

Tell the class: pencils ready during the watch, not only after. A 1–2 minute mid-demo jot is enough: tick or sketch solid / soft / puddle for each material as change appears. Full sentences come later in the record step.

Modelled investigation cycle (say this aloud)

I wonder: will gentle warmth melt all three, or only some?

I predict: (point back at the journal predictions) I think the ice will melt fairly quickly, the chocolate and butter will soften and may melt, and none of them will stay completely unchanged.

I test: I leave all three dishes on the same warm tray for the same time so the only difference is the material itself.

I observed (typical result): the ice usually melts first into clear water; chocolate softens then pools; butter softens and may melt to a yellow liquid. Times vary with how warm the water is, but ice almost always goes first.

I think: gentle heat can melt some solids into liquids. The material is still there; it has changed state.

If melting is slow (pacing fallback)

• If little has changed after a few minutes, refresh with warmer (still hand-safe) water from the jug.
• Teach from what is visible: soft edges, gloss on chocolate, water starting to pool under ice. You do not need full puddles of all three to land the idea of melting.
• If chocolate is still slow, note that for next time a smaller piece helps; keep pieces similar today for a fair look.
• Wipe any drips at once so the floor stays safe.

Key questions while they watch: What is changing first? Is the chocolate still chocolate? Which edges went soft? Does this match what you predicted?

Lift the shallow tray out of the warm water (or move the three dishes onto a cool plate) so cooling can begin. Keep pupils in the viewing arc with journals open for a quick cool jot (symbols fine). Keep the board to watch prompts only while they look; do not announce typical outcomes on the IWB yet.

Pace the wait with short whole-class look-fors so there is no dead air while change is slow:

• Minute 1–2: Look at the edges of the butter. Anything firmer than before?
• Minute 3–4: Is there a thicker or dull top on the chocolate pool?
• Minute 5–6: Which dish still looks most like a puddle? Has the ice water gone solid again?

After they have looked, land results and the word by talk (not on the board during the watch): Butter often begins to firm at the edges; chocolate may thicken or dull on top as it cools; the melted ice usually stays liquid water here. If a change can go back, we call it a reversible change. Butter setting again is one example. Water staying liquid here is still useful evidence: the reverse step for ice needs colder conditions.

What to expect: butter often begins to firm at the edges within several minutes; chocolate may thicken or dull on the surface as it cools; the melted ice stays liquid water in a normal classroom and will not refreeze without a freezer or very cold place. Only claim what the demo can show in this slot. Water staying liquid is the planned teaching point, not a failed reverse.

If you have freezer access later in the day, you may show one cup of the melt water frozen again as a follow-up, or simply tell the class that is how the reverse step is finished for water.

Misconception: some children think only ice is "allowed" to reverse. Butter and chocolate setting again on cooling are also everyday reversible changes (solid to liquid and back), even if the set solid looks a slightly different shape.