Medical Detectives · Case File No. 002

The Science
Fair

Five experiments. One blue ribbon. Four hidden flaws. Can you find them?

Case type: Experimental Design · Difficulty: Detective, 2nd grade · You will need: the Case 2 Worksheet and everything you learned in Activity 1.2.

The scene

Saturday morning.
The gym.

It is the Westbrook Middle School Science Fair. Five students entered the Health & Body category. Every one of them ran an experiment, made a poster, and wants the blue ribbon.

The judges called in sick. You are the judges now. Four of the five experiments have a serious flaw hidden in the design. One is done exactly right.

The rule of the fair: the best-looking poster does not win. The best-designed experiment wins — even if its result is boring.

Your evidence toolkit · from Activity 1.2

The judge's checklist

A trustworthy experiment has all eight of these. Check every entry against every one.

1

Question

Specific and testable. You could measure the answer.

2

Hypothesis

A prediction with a reason — not just a guess.

3

Independent variable

The ONE thing the scientist changes on purpose.

4

Dependent variable

The thing that is measured — with units.

5

Control

Something to compare against: a before-number, or a group that gets nothing.

6

Fair test

Everything else stays the same. Change one thing at a time.

7

Procedure

Numbered steps with exact amounts and times, so a stranger could repeat it.

8

Trials

Repeat it and average. One try can be luck.

Miss one of these and the result cannot be trusted — no matter how exciting it looks.

Procedure

How to judge
the fair

  • Read all five posters. Do not decide anything yet.
  • For each entry, find the independent variable, the dependent variable, the control, and the number of trials. Write them on your Case 2 Worksheet.
  • Ask: is it a fair test? Could a stranger repeat it?
  • Name the one major flaw — or say why there is none.
  • Give the blue ribbon, with evidence.

Rookie mistake: picking the entry whose result "worked." A result you cannot trust is not a result. Judge the design, not the ending.
Stations: the five posters are also printable cards (the 🗂 Stations button) so groups can rotate table to table.

Exhibit A · Entry 1 of 5
Does calm music lower your heart rate?Priya N. · Grade 7
Question
Does listening to calm music lower a person's heart rate?
Hypothesis
Calm music will lower heart rate, because music helps people relax.
Independent variable
Listening to calm music
Dependent variable
Heart rate, in beats per minute (bpm)
Control
The partner's resting heart rate before the music
Materials
Chair, phone with a calm playlist, stopwatch, data table, 3 partners
Procedure
  1. Partner sits in a chair for 2 minutes, feet on the floor.
  2. Count the pulse for 15 seconds and multiply by 4. Do this 3 times. Average.
  3. Turn on the calm playlist. Turn off the lights, close the curtains, and have the partner close their eyes and breathe slowly for 2 minutes.
  4. Count the pulse again 3 times. Average.
  5. Repeat with 2 more partners.
Data
Table: before average and after average for each partner, in bpm.
Result
All 3 partners' heart rates went down 8–12 bpm. "Calm music works!"
Westbrook Middle School Science Fair · Health & Body · This is a practice entry with fictional students.
Exhibit B · Entry 2 of 5
Which hand sanitizer kills the most germs?Diego R. · Grade 6
Question
Which of three hand sanitizers (Brand A, B, or C) leaves the fewest bacteria on a hand?
Hypothesis
Brand A will leave the fewest bacteria, because its label says it has the most alcohol.
Independent variable
The brand of sanitizer (A, B, or C)
Dependent variable
Number of bacteria colonies on the agar plate after 2 days
Control
I used the same amount of sanitizer — 2 pumps — every time.
Materials
3 agar plates, Brand A, B, C sanitizer, tape, marker, PPE
Procedure
  1. Rub 2 pumps of Brand A on your right hand for 20 seconds.
  2. Press your fingertips on agar plate A for 5 seconds. Close and tape it.
  3. Repeat steps 1–2 with Brand B on plate B, then Brand C on plate C.
  4. Store all plates upside down for 48 hours.
  5. Count the colonies on each plate.
  6. Repeat the whole thing 3 times with fresh plates.
Data
Table: colonies counted for A, B, and C in each of the 3 rounds, plus averages.
Result
A: 4 colonies · B: 6 · C: 5. "Brand A wins!"
Westbrook Middle School Science Fair · Health & Body · This is a practice entry with fictional students.
Exhibit C · Entry 3 of 5
Does one minute of slow breathing lower heart rate?Amara O. · Grade 6
Question
Does one minute of slow breathing lower a resting person's heart rate?
Hypothesis
Slow breathing will lower heart rate, because slow breathing signals the body to calm down.
Independent variable
One minute of slow breathing (in for 4 counts, out for 4 counts)
Dependent variable
Heart rate, in beats per minute (bpm)
Control
Resting heart rate before the breathing — 3 trials, averaged
Kept the same
Same chair, same quiet room, lights on, no music, feet on the floor, same 15-second count × 4, same partner counting
Safety
Only healthy participants with no breathing problems.
Procedure
  1. Participant sits in the chair, feet flat, quiet, for 2 minutes.
  2. Count the pulse for 15 seconds. Multiply by 4. Record in bpm.
  3. Repeat step 2 two more times. Average the three = baseline.
  4. Participant breathes slowly for one minute: in 4 counts, out 4 counts.
  5. Immediately count the pulse for 15 seconds × 4. Record.
  6. Repeat steps 4–5 two more times. Average the three.
  7. Repeat steps 1–6 with 4 more participants (5 total).
Data
Table: 3 before and 3 after trials per participant with averages, in bpm; plus observations.
Result
Average dropped from 84 to 79 bpm across 5 people. "Slow breathing lowers heart rate a little."
Westbrook Middle School Science Fair · Health & Body · This is a practice entry with fictional students.
Exhibit D · Entry 4 of 5
Does ice water lower your body temperature?Kenji T. · Grade 7
Question
Does drinking a glass of ice water lower body temperature?
Hypothesis
Ice water will lower body temperature, because the water is cold.
Independent variable
Drinking one glass (8 oz) of ice water
Dependent variable
Forehead temperature, in °F
Control
My temperature before drinking the water
Kept the same
Same thermometer, same room, same chair, measured from the same distance
Materials
No-touch forehead thermometer, 8 oz glass, ice water, clock
Procedure
  1. Sit in the chair for 5 minutes.
  2. Measure my forehead temperature. Record it.
  3. Drink one 8 oz glass of ice water in under 2 minutes.
  4. Wait 5 minutes.
  5. Measure my forehead temperature again. Record it.
  6. Compare the two numbers.
Data
Before: 98.4 °F  ·  After: 98.1 °F  ·  Participants: 1 (me)  ·  Trials: 1
Result
"It went down 0.3 degrees. Ice water lowers body temperature!"
Westbrook Middle School Science Fair · Health & Body · This is a practice entry with fictional students.
Exhibit E · Entry 5 of 5
Does jogging raise your breathing rate?Lucas M. · Grade 6
Question
Does jogging make a person breathe faster?
Hypothesis
Jogging will raise breathing rate, because the body needs more oxygen when it works hard.
Independent variable
Jogging
Dependent variable
Breathing rate
Control
My partner's breathing before jogging
Kept the same
Same partner, same track, same day
Materials
A partner, the school track, a clipboard
Procedure
  1. Count my partner's breaths for a while.
  2. Have my partner jog around the track for a bit.
  3. Count breaths again.
  4. Write down whether it went up.
  5. Do it a few times.
Data
Before: "normal"  ·  After: "a lot more"  ·  (no numbers written down)
Result
"Breathing went up every time. Jogging raises breathing rate!"
Westbrook Middle School Science Fair · Health & Body · This is a practice entry with fictional students.
Crack the case

Questions a judge asks

Clue 1 · One thing at a time
Between the before and the after, how many things changed? If more than one changed, which one caused the result?
Clue 2 · Compared to what?
What is each entry comparing against? Is that a real control — or just something kept the same?
Clue 3 · Could you repeat it?
Read each procedure as if you had to do it tomorrow. How long? How many? Which units? If you have to guess, so would every other scientist.
Clue 4 · How many times?
One person, one try — could the result be luck, or the thermometer's normal wobble? How many trials would convince you?
Deliver your verdict

Who gets the
blue ribbon?

On the Case 2 Worksheet, fill in the judge's table for all five entries. Then, for each one, name the major flaw and how to fix it — or say why the design is sound.

  • Sentence starter: "The biggest flaw is ______, so we cannot tell ______."
  • Then: "To fix it, the scientist should ______."
  • Finally: "The blue ribbon goes to Entry ___ because ______."

Remember: exactly one entry has no flaw. If you found flaws in all five, look again — one of your "flaws" is not really a flaw.

Debrief · after the worksheets are in

The verdicts

Judges, compare your rulings first. Then the teacher opens the envelope.

Entry 1 · Priya
Not a fair test

Music, dark room, closed eyes AND slow breathing all changed at once. Three independent variables — the result could be any of them.

Entry 2 · Diego
No control

"Two pumps every time" is a constant, not a control. Without a no-sanitizer plate, we cannot tell whether any brand did anything at all.

Entry 3 · Amara
🏆 Blue ribbon

One variable, a real before-baseline, everything else held the same, exact steps with units, 3 + 3 trials, 5 people — and an honest, small result.

Entry 4 · Kenji
One trial, one person

A 0.3 °F change from a single reading is inside a forehead thermometer's normal wobble. Repeat it, average it, add people.

Entry 5 · Lucas
Cannot be repeated

"For a while," "for a bit," "a few times," no units, no numbers. Nobody could redo it — and "a lot more" is not data.

Closing the case

Why judges
matter

Every medicine you will ever take was tested with these same eight parts. Before a doctor trusts a study, they ask exactly what you asked today: one variable? a control? could it be repeated? how many trials?

A flashy result with a broken design is worth nothing. A small, honest result from a sound design is worth a blue ribbon.

Turn in your worksheet, judge. Next time you design an experiment, run it past this checklist first — be your own toughest judge.

Word Bank · Banco de Palabras

Tap a word for the full card.

Case 2 — Slide Index

— SLIDE 01/13