Nonograms in the classroom: lesson plan, difficulty ladder and the free classroom pack (ten A4 sheets in hand-out order, desk page, record sheet, answer key) · blobsmith.lbwma.com/nonograms-in-the-classroom
A nonogram is a logic puzzle that ends in a picture — which means a pupil knows they got it right before you say so. This page is the part nobody publishes: which sheet to give first, what each one actually costs in class time, and why one defect makes this activity fail in a room of thirty even though it is invisible on the page.
The numbers beside a row give the lengths of the runs of filled cells, in order, with at least one empty cell between runs. Everything else follows from that — and the technique that solves most of a grid is a piece of arithmetic a pupil can be made to do explicitly.
Take a run of k filled cells in a line of n. Push it as far left as it goes, then as far right: the cells covered both times are certain. How many? 2k − n.
| run (k) | cells guaranteed | the sum |
|---|---|---|
| 5 | — | nothing: 2×5 − 10 ≤ 0 |
| 6 | 2 | 2×6 − 10 = 2 |
| 7 | 4 | 2×7 − 10 = 4 |
| 8 | 6 | 2×8 − 10 = 6 |
| 9 | 8 | 2×9 − 10 = 8 |
| 10 | 10 | 2×10 − 10 = 10 |
That table is worth a lesson on its own: it is a formula, it has a threshold (below 6, in a line of 10, it yields nothing), and a pupil can check every row of it by hand against a grid. Then the rest of the puzzle is pure deduction — what must be true, what cannot be — with a picture at the end as the reward.
The full student-facing explanation, with the other three deductions drawn out, is on how to solve nonograms. It prints as a handout.
Most free nonogram PDFs are generated in bulk and never solved. That produces puzzles which are not solvable by reasoning: at some point the only way forward is to pick one of two possibilities and backtrack if it goes wrong. Nothing on the sheet tells you which puzzles those are.
Alone at a kitchen table that costs an evening. In a classroom it is worse, and it fails in a specific way: the pupils who most need the win are the ones who conclude they are bad at it, while the confident ones start guessing — which is the exact habit the activity was supposed to replace. You cannot rescue it mid-lesson, because you can't tell them where the deduction is, because there isn't one.
Every sheet in the pack on this page goes through a solver before it is allowed into the file. It is rejected if it does not close on row-and-column logic alone, if a second grid satisfies the same numbers, or if the closed grid isn't exactly the picture that was drawn. Failures are thrown out, not patched. 10 of 10 pass — and that is re-proven on the shipped bytes every time this page is rebuilt, not asserted once in a blurb.
The practical consequence for you: any pupil who is stuck is stuck on something findable. There is always a decidable cell somewhere on the grid, so "look for a different row" is honest advice and always works.
Not by grid size and not by feel. Each sheet was run through the solver, and two numbers come out of it. Passes is how many times you have to sweep the whole grid — rows, then columns, then rows again — before it closes: it is how long the sheet drags. First sweep is how many cells fall out of the very first pass over the rows, which is whether a pupil gets traction in the first few minutes or stares at an empty grid.
| Hand out | Picture | Grid | Passes to close | First sweep opens | In the general free pack |
|---|---|---|---|---|---|
| 1 | lantern | 10×10 | 3 | 66 of 100 (66%) | Puzzle 4 |
| 2 | clock | 10×10 | 3 | 56 of 100 (56%) | Puzzle 5 |
| 3 | paw | 10×10 | 3 | 46 of 100 (46%) | Puzzle 3 |
| 4 | snowman | 15×15 | 3 | 102 of 225 (45%) | Puzzle 6 |
| 5 | snowflake | 10×10 | 3 | 20 of 100 (20%) | Puzzle 2 |
| 6 | gift | 10×10 | 3 | 2 of 100 (2%) | Puzzle 1 |
| 7 | gamepad | 15×15 | 4 | 170 of 225 (76%) | Puzzle 9 |
| 8 | robot | 15×15 | 4 | 107 of 225 (48%) | Puzzle 7 |
| 9 | alien | 15×15 | 5 | 120 of 225 (53%) | Puzzle 8 |
| 10 | hot air balloon | 20×20 | 7 | 120 of 400 (30%) | Puzzle 10 |
That is the order the classroom pack is already in — Sheet 1 is lantern, Sheet 10 is the 20×20. The last column is only there for anyone who already downloaded the general pack from the free nonograms page, where the same ten sheets are numbered in the order they were drawn instead. The five 10×10s all close in at most 3 passes, which is what makes them the right size for a single period; the 20×20 takes 7 and is not a whole-class sheet.
A plan, not a prescription — but the sheets it names are chosen by the numbers above rather than at random.
Draw an empty line of ten cells and write the clue 7 beside it. Ask where the run could start. Establish that it doesn't matter — the middle 4 are filled either way. That single example is the entire technique they need for the first sheet.
Project Sheet 1 and do only the rows, out loud, one at a time. Nothing else — no columns yet. By the end of that sweep 66 of 100 cells are decided, which is what convinces a room that this is not guesswork.
Hand out the next sheets in the ladder above. Pairs, not alone: the arguing is the lesson — one pupil claims a cell must be filled, the other has to accept or refute it. Your only intervention is "which row have you not looked at since you last wrote something?", because the new information is always in the line crossing the last cell they filled.
Anyone who finishes early gets Sheet 10, the 20×20 — 7 passes, and it will not be finished in the lesson, which is the point of it. Nobody has to finish anything: an unfinished grid is still 66%+ of a grid of proofs. The answer key is on the last pages of the PDF, and it is worth showing the picture even to a pupil who didn't get there.
The 100 in the book go through the same solver as the ten free ones, and none of the free ten are repeated in it — so a class that gets through the pack has a whole year of sheets behind it, and you don't pay for anything twice.
How to solve nonograms — the four deductions, drawn, as a pupil handout · the solver — paste the clues of a sheet a pupil made and check it closes before you photocopy it · the checker — a pupil draws their puzzle in it and finds out on the spot whether it can be solved without guessing · the same ten, playable in a browser — for a tablet lesson, or for the pupil who finishes early · the free pack · in Portuguese: como resolver nonograma