Make "the substance stays the same" visible with particle diagrams and a forward/back arrow motif.
Particle before-and-after
For each station, students draw the particles before and after the change using the same coloured circles in both pictures — only their arrangement changes. Seeing identical circles either side proves the substance is unchanged. This mirrors the animated states-of-matter diagram in the deck.
The two-way arrow
Teach reversible change with a double-headed arrow (⇔) between the before and after pictures. Students label the forward arrow ("melt") and the backward arrow ("freeze"). The two-way arrow becomes the visual signature of a reversible change — and its absence will mark irreversible change next lesson.