Title
A lesson about what we can measure, what follows from it, and what does not.
Ages 12–18 · 45–60 minutes
Materials: Paper, pens, and the source table at /global-data
A lesson about what we can measure, what follows from it, and what does not.
Teacher notes
Set the frame before any content: this lesson is about reading evidence, and microplastics are the worked example. Students who leave able to interrogate a particle count have got the point, even if they forget the numbers.
Slide 1 of 9
Objectives
Teacher notes
Read these aloud, or put them on the board for the whole lesson. Objective 4 is the one that carries beyond the topic — it is the assessable outcome.
Slide 2 of 9
Starter · 5 minutes
One instrument sees particles down to 100 µm. Another sees down to 1 µm. Should their totals be compared as if they counted the same thing? Why?
Teacher notes
Write the three values on the board before showing the question. Let the disagreement run — the answer they arrive at themselves is the spine of Activity 3. Do not resolve it yet.
Slide 3 of 9
Activity 1 · 10 minutes
In groups: sketch each form and add one plausible source.
Shape alone does not chemically confirm that a suspected particle is plastic.
Teacher notes
Expect confident misidentification — that is the useful part. When a group is sure something is plastic, ask what instrument would be needed to settle it. Bead versus fragment is the distinction worth pressing: it separates a design decision from a failure.
Slide 4 of 9
Activity 2 · 15 minutes
At every arrow, mark three things:
Teacher notes
The third mark is the hard one and the one to insist on. Students will confidently rank pathways; ask what they would have to measure locally to defend the ranking. Wastewater treatment is a good example — capture is high, but what is captured moves into sludge rather than disappearing.
Slide 5 of 9
Activity 3 · 15 minutes
Take two rows from the source table at /global-data and fill this in.
| Question | Study A | Study B |
|---|---|---|
| What was sampled? | ||
| Where and when? | ||
| Particles per litre | ||
| Lower size limit | ||
| Identification method | ||
| Mean, median or range? |
Which differences could change the reported count? Can either row support a country ranking?
Teacher notes
The answer to the second question is no, and students should be able to say why: different size limits and methods, no shared sampling frame. This is where the starter question gets settled.
Slide 6 of 9
Discussion · 5 minutes
What new evidence would move an emerging or uncertain claim?
Teacher notes
Students often read 'uncertain' as 'untrue'. It means the study needed to settle it has not been done. Ask what that study would have to look like.
Slide 7 of 9
Exit ticket
Teacher notes
Sentence 3 is the assessment. Anything naming risk, harm or dose from a detection study alone has missed the lesson and is worth revisiting next session.
Slide 8 of 9
Guardrails
Teacher notes
These are the four ways this topic usually goes wrong in a classroom. The second is the most common: a count of particles is not a dose, and a dose is not a harm.
Slide 9 of 9