Number Detectives: Cracking the Code of 3-Digit Comparisons
Shared by A STEM Educator
Students will compare and order pairs and sets of 3-digit numbers up to 1,000 using place-value reasoning (hundreds first, then tens, then ones) and record comparisons with the relational symbols , , and .
Lesson Overview
Students work in random groups at vertical surfaces to discover place-value hierarchy as the key to comparing 3-digit numbers, progressing from comparing hundreds digits to solving open-ended missing-digit inequalities. The space-mission framing positions each group as a crew navigating by number magnitude.
Materials
- Vertical whiteboards or large chart paper taped to walls
- One dry-erase marker per group (forces collaboration)
- Erasers or socks
- Random group generator (cards, sticks, or app)
- Printed 'Mission Cards' with thin-slice tasks
- Place-value reference chart (hundreds/tens/ones columns)
- Exit slip half-sheets
- Optional: tablet or laptop for Desmos interactive tool
Scaffolded Task Progression
Your crew must choose the safer asteroid path. The path with the LARGER number is safer.
Compare each pair. Write , , or .
On your whiteboard, show HOW you know which is larger.
Now the numbers have tens and ones — but the HUNDREDS still settle it.
Compare each pair. Write , , or . Show your place-value thinking.
Big Question for your crew: Do you even need to look at the tens or ones? Why or why not?
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