Thermometer puzzles for kids and classrooms
Thermometer puzzles have tiny rules, need no arithmetic beyond counting, and scale from a 4×4 grid to a 15×15 challenge. That makes them a good fit for teaching how to reason step by step.
Part of the complete guide to thermometer puzzles · guide 6 of 7
Why thermometer puzzles work well for learning
- Short rules, real reasoning. Fill from the bulb, no gaps, match the counts. Everything else is logic.
- Every step can be justified. Each cell is decided for a reason ("row 3 is already full"), which makes the puzzle a natural way to practise explaining thinking out loud.
- No guessing. Every puzzle on this site has one solution reachable by logic (here is how we make sure), so a student who is stuck knows there is a reason to find.
- Easy to differentiate. Six grid sizes and two styles give a smooth path from beginner to expert.
Skills students practise
| Skill | Where it shows up in the puzzle |
|---|---|
| Deductive reasoning | Deciding a cell only when the clues force it |
| Counting and comparing | Checking how many cells a row still needs and can still hold |
| Rules and constraints | Respecting "fill from the bulb, no gaps" |
| Cause and effect | Seeing one filled cell force others along the tube |
| Proof by contradiction | "If this cell were filled, row 4 would have too many", for older students |
| Persistence | Working through larger grids without guessing |
A 45-minute lesson plan
Before the lesson
Print one 4×4 sheet per student (and some 6×6 sheets for fast finishers), with answer keys for yourself. Optionally, display the how-to-play page on a projector.
1. Hook (5 minutes)
Draw a thermometer on the board and ask: "If the temperature rises, where does the liquid go first?" Agree that it always starts at the bulb and rises without gaps. That is the whole first rule.
2. Rules together (10 minutes)
Show this 4×4 puzzle and explain that the numbers count filled cells in each row and column. Solve the first two steps together, asking students to justify each one.
The full walkthrough of this puzzle is in how to play.
3. Pairs practice (20 minutes)
Students solve 4×4 puzzles in pairs. One partner proposes a move and the other must agree it is forced before it is drawn. Pairs who finish move on to 6×6.
4. Share and reflect (10 minutes)
Ask pairs to share one move they were sure of and explain why. Use the discussion questions below.
Discussion questions
- Which clues were the easiest to start with? Why?
- If you know one cell is filled, what else do you know straight away?
- How did you check your answer was correct?
- Did you ever want to guess? What did you do instead?
- Older students: can you explain why the row clues and column clues add up to the same total? (The answer is in the math of thermometer puzzles.)
Differentiation
- Support: start with 4×4 and point out the rows or columns with 0 or full clues. Let students use the online game with Highlight rule breaks switched on.
- Core: 6×6 straight puzzles, solved without hints.
- Stretch: 6×6 or 8×8 curved puzzles, or ask students to explain a step using the squeeze.
- Challenge: have students design their own 4×4 puzzle and check that a partner can solve it without guessing. Classes that already know nonograms or Battleships can compare the rules using this comparison.
At home
For families, the daily puzzle makes a short shared routine. Start with the 4×4 together, then let children try the 6×6 on their own. Progress saves automatically in the browser, with no account or personal details needed. See our privacy policy.
Questions
What age are thermometer puzzles suitable for?
Do students need to know any math?
Can students play online instead of on paper?
Print a class set
Generate 4×4 or 6×6 sheets with answer keys.