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Session 3 of 8
Collecting
Data
We have a great question. Now let's go get the data — carefully and consistently.
Data Science for Young Minds · Grade 3
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Today's Plan
What We're Doing Today
- Share data questions from Session 2
- Three ways to collect data
- | | | ̶| Tally marks — the data collector's best friend
- Mini-Survey — survey 10 classmates!
- Counting & measuring carefully
- Error Detective — what went wrong?
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Warm-Up
You Wrote a Data Question!
In Session 2, you designed a data question that's fair, specific, and answerable.
"Who wants to share their question?"
2–3 volunteers share. Quick class vote: "Is this a good data question? Thumbs up or down?"
Today — you'll actually USE that question to collect real data from your classmates!
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Lesson 1
Three Ways to Collect Data
Survey
Ask people questions. Best for opinions and preferences.
Observation
Watch and record what you see. Best for behavior and events.
Measurement
Use tools for exact numbers. Best for size, weight, time.
The method you choose depends on your question. Different questions need different collection methods!
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Lesson 1
Which Method Fits?
Match the question to the right collection method:
- "What is your favorite fruit?" → Survey — ask people
- "How many cars pass our school in 10 minutes?" → Observation — watch & count
- "How tall is each student in the class?" → Measurement — use a ruler/tape
- "How many students bring lunch vs. buy lunch?" → Observation — watch at lunchtime
- "How long does it take to read one page?" → Measurement — use a timer
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Lesson 2
Tally Marks — Fast Counting
Tally marks let you count quickly while you're busy listening or watching.
|1
| |2
| | |3
| | | |4
||||̶5 ← cross!
||||̶ |6
||||̶ ||||̶10
The 5th mark crosses the group of 4. Groups of 5 make it easy to count at the end — just count groups and add!
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Lesson 2
Survey Rules — Consistency!
The most important word in data collection: CONSISTENT. Same method, every time.
- Ask the question exactly as written — no changing words mid-survey
- Give all the answer choices — don't hint at which one is "right"
- Record with a tally mark immediately — don't trust your memory
- Each person gets asked only once
- Say "thank you" — be a respectful data collector!
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Activity!
Mini-Survey Time
Grab your worksheet, your clipboard, and your pencil. You have 12 minutes to survey 10 classmates.
- Use YOUR data question from Session 2
- Record answers using tally marks
- Follow the 5 survey rules
- Don't ask the same person twice!
Ready? Go collect some data!
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Tally Count Challenge!
Your teacher will write some tally marks on the board.
First team to call out the correct count wins!
Remember: count the groups of 5 first, then add the leftovers.
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Lesson 3
Counting & Measuring Carefully
Careful Counting
- Point to each item as you count
- Move counted items to a separate pile
- Count again if not sure
- Write down as you go — don't rely on memory
Precise Measuring
- Start from zero — not the edge of the ruler
- Always include the unit (cm, inches, seconds)
- Measure twice if the number seems surprising
- Record the number AND the unit together
Without units, "7" means nothing. Is it 7 cm? 7 feet? 7 minutes?
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Lesson 4
When Things Go Wrong
Every data collector makes mistakes. Here are the most common ones — and how to avoid them:
Changing the question mid-survey → Your data isn't comparable anymore
Forgetting to record an answer → You lose data forever
Asking someone twice → That person counts double, distorting results
Forgetting units when measuring → "7" alone is meaningless
Fix all of these by: preparing your recording sheet BEFORE you start, and following your collection rules consistently.
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Error Detective
Spot the Mistake!
Your teacher will read 3 scenarios. For each one — what went wrong?
- Scenario 1: Mia records some answers as words and some as tally marks.
- Scenario 2: Sam keeps telling respondents "most people say pizza, just so you know."
- Scenario 3: Dev accidentally asks his best friend the same question twice.
Use your worksheet Part 3 — write the error AND how to fix it.
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Reflection
How Did Your Survey Go?
"What was the hardest part of collecting data today?
What would you do differently next time?"
2–3 students share. Common answers:
- People kept giving answers that weren't one of the choices
- I forgot to tally once
- It was hard to ask and write at the same time
- Someone asked me to repeat the question
All of these = real data science challenges. You just experienced what researchers deal with!
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Vocabulary Review
Words to Know
Survey
Asking people questions to collect data
Observation
Watching and recording what you see
Measurement
Using tools to get exact numbers
Tally mark
A line used for fast counting — 5th mark crosses
Consistency
Recording the same way every time
Collection error
A mistake that makes data unreliable
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Wrap Up
Session 3 Complete!
- Three collection methods: survey, observation, measurement
- Tally marks group in 5s for fast, accurate counting
- Consistency = record the same way every time
- You collected real data from real people today!
- Errors happen — knowing them helps you avoid them
Coming up — Session 4: All that data you collected is messy! Next session we organize it into tables and frequency charts so the patterns can appear.