Logic puzzles in the classroom: a practical guide to a deduction session

What it actually trains

It is worth being precise, because "logical reasoning" says nothing. One of these cases asks for four concrete things, and asks for them all at once.

Deducing by elimination. You do not progress by finding where somebody is, but by ruling out where they cannot be. It is the step that is hardest to teach, and here it is practiced on every move: each person placed crosses out an entire row and an entire column.

Reading precisely. Every word on a card counts. "Next to" means the adjacent square and inside the same room: two touching squares separated by a wall do not count. Skim-readers get it wrong, and find out on their own.

Justifying. This is the good one. The question that turns the activity into a lesson is not "who did it?" but "how do you know they were there?". Because the solution is unique and forced, an answer always exists and can always be checked. There is no room for opinion.

Finding your way around a grid. Rows, columns, above, to the left, inside and outside a room. It gets worked on without ever being named.

What age it works from

The only real requirement is reading a short sentence and understanding it. No sudoku experience, no times tables, no previous logic puzzles.

With the small plans and few suspects it works in elementary school: they are solved in a few minutes and the reasoning fits on a whiteboard. The big plans, with more people and clues that refer to each other, are middle school and up — and the teachers' lounge puzzle club, which is usually where the real arguing happens.

In libraries and nursing homes the same thing happens with the ages swapped: a small case sits well on a table and gets solved in company, out loud.

A half-hour session, step by step

What follows is built for a one-off lesson, with no preparation and no screens.

Five minutes of rules. There are four, and they are better taught by solving one tiny case in front of everyone than by explaining: one person per row and column; the cards tell the truth; squares with furniture cannot be occupied; whoever ends up in the victim's room is the murderer.

Fifteen minutes on the case, in pairs. Pairs beat solo work: it forces them to say out loud why a square gets crossed out, which is exactly what you want to hear. One pencil per pair, and an eraser.

Five minutes of comparing notes. Before handing out the solution, have somebody explain the first step: which card they attacked first and why that one. That is where you see who understood the method and who got lucky.

Five minutes of solution. The solution PDF comes with the reasoning written alongside, not just the filled-in grid: read it out and compare it with what each pair did.

Handling different speeds

The trick is not to change subject but to change size. The same setting exists at several levels: whoever finishes early does not sit staring at the ceiling, they take the big case from the same place and carry on with the same rules.

And because the solution is a separate PDF, you can hand it out at the end or leave it on a table at the back for anyone who wants to mark their own work. That removes half the raised hands.

If someone is completely stuck, the way out is not to give them the murderer: ask them which card in front of them is the most specific. Nine times out of ten they have not looked at it.

The material: free, with written permission

Printable cases are ready to photocopy, free and with no sign-up. Each one comes as three files: in color, in black and white — the one that actually gets printed, because it does not eat the ink — and the solution as a separate PDF, so you hand it out when you choose and not before.

And the permission, which is what you need before taking anything into a classroom: free to print and hand out in classrooms, libraries and nursing homes. All we ask is that the credit stays: sudokudetective.com. It is written on the download page itself, so you can show it to anyone who asks.

They exist in all seven languages of the site, which doubles as a language lesson: the same case in two languages, with the vocabulary of a house and of positions.

Three details that save half the questions

Explain "next to" before you start, and draw it. It is the one rule that gets misread, and once said it never comes up again.

Insist on crossing out in pencil. Anyone who does not mark the crosses tries to hold it all in their head, gets stuck and gives up. The ones who cross out get through.

Do not hand out the solution with the case. It sounds obvious and it is not: if it is on the table, it gets looked at. Better at the back of the room, or at the end.

And if the group gets hooked: the book

When a case works in class, somebody always asks where there are more. The long answer is Sudoku Detective: a paperback, in full color, with illustrated settings and the solution to every case explained step by step. It is classroom-library material and it makes a good end-of-year present; the cases in the book are its own and are not on the website.

The short, free answer: it plays in the browser, no account and nothing to install, with new cases every week, and here are the full rules with one case solved end to end, in case you want to read them before the lesson.