Lean on the visual nature of graphing, and make the line vs bar choice and the evaluation visible.
Line vs bar at a glance
Show the same data plotted both ways — as a line graph and as a bar graph — and have students decide which suits continuous data. Seeing a jagged bar chart next to a smooth trend line makes clear why continuous data (foil length) wants a line. Colour the "correct choice" green.
Annotate the trend
On their finished line graph, students draw an arrow along the slope and label it in words ("as foil length increased, brightness decreased"). Turning the visual slope into a sentence bridges graph-reading and conclusion-writing, mirroring the deck's animated line graph.
Evaluation as a checklist
Provide the fairness evaluation as a visual checklist (✓/✗ against each controlled variable) so students can see at a glance where the test held and where it slipped.