How to teach a child sudoku: where to start

Rather than an age, look for three concrete signs. A child is ready if they can:

• recognise the digits 1 to 4 — naming them is enough, they don't need to write them;
• understand "only once" — that is the whole rule of sudoku, and the only abstract idea in the game;
• stay with one activity for five to ten minutes — which is how long a 4×4 grid takes.

In practice that usually lands somewhere around ages five to seven, but the gap between two children of the same age is wide enough that the number means very little. The real test takes two minutes: open a 4×4 grid and see whether your child grasps that a digit already sitting in a row cannot go anywhere else in that row.

One detail helps younger children enormously: on Sudoku-Land, every digit has its own colour. A child still hesitant about reading numbers can reason in colours — "the green one is missing from this box" — and reach the answer by exactly the same logical route. That alone often makes it possible to start a year or two earlier than expected.

There is no need for a lesson. One sentence does it: each digit once per row, once per column, once per box.

Two things make it stick:

• Phrase it as something forbidden, not as an instruction. "The same number twice in one row isn't allowed" is far clearer to a child than "each digit appears exactly once".
• Show it once instead of explaining it twice. Deliberately place a duplicate digit in front of them and let them spot the problem. A rule they have seen sticks; a rule recited at them does not.

After that, get them into the habit of tracing three directions with a finger before placing a digit: the row, the column, the box. Those three gestures are the complete beginner's reasoning. After a few games they do it with their eyes, without moving a hand.

This is the choice that decides everything. A 9×9 grid means keeping track of 27 zones (9 rows, 9 columns, 9 boxes) with nine digits in play. A 4×4 means 12, with four digits. They are not the same activity, and starting too high is the surest way to put a child off the game in a single sitting.

The three sizes built for learning, in order:

The step from 4×4 to 6×6 matters more than it looks: the box stops being a square and becomes a three-by-two rectangle. Plenty of children keep hunting for a square that no longer exists, and get it wrong for that reason alone. Point out the box borders once and the problem disappears.

Each size also offers three difficulty levels — Easy, Medium, Hard — which change how many digits you start with and how many help uses you get (5, 3 then 2 on the 4×4; 3, 3 and 2 on the other two).

Sooner or later a child will sit in front of a grid with no idea what to do next — and that is the moment most adults give the answer. On the Kids, Junior and Junior+ grids, the 🆘 Help button exists to avoid exactly that: instead of revealing a digit, it opens a panel below the grid that animates the reasoning, cell by cell, showing where the digit goes and, above all, why.

Each stage takes one click on ⏭ Next step: the digit involved grows and turns red, then its row, column and box turn red in turn — the area that is precisely what stops it going anywhere else. Here is the full sequence, captured on a real game:

The number of help uses stays capped by the difficulty chosen, and the grid remains fully visible throughout: this is not a window covering it, just a panel opening underneath. The child watches the reasoning unfold on their own grid, not on some worked example.

The useful habit, on the adult side: let them trigger the help themselves, then ask them to explain back what they just saw. Putting it into their own words is what makes the technique stick — watching it does not.

An answer handed over solves the immediate problem and teaches nothing for the next one. It is tempting because it is quick, but the child walks away with one filled cell and no method — and gets stuck again three cells later, in an identical situation.

Showing the reasoning costs thirty seconds more and changes what follows: which area is already taken, why only one cell is left. It is the same logic used on the 9×9 grids at higher levels — see How to play for the full set of techniques, and the complete method for the order to look for them in.

In practice it comes down to one measure: the number of help uses per grid should fall as the games go by. If it doesn't, the puzzle is too hard — drop back a level rather than pushing on.

Three signs, and you want at least two of them:

• they finish a grid without using any help, two or three times in a row;
• they no longer check row, column and box one at a time — they see the cell straight away;
• they are bored, which is the most reliable signal of the three.

Before changing size, move up in difficulty on the size they are already on: going from Easy to Medium on a 4×4 is a much smaller step than going from a 4×4 to a 6×6, and it is often enough to bring the interest back.

And if the bigger size doesn't take, dropping back is not a failure — it is the right call. A grid abandoned halfway leaves a far more lasting impression than an easy one finished.

• Starting with a 9×9 "just to see". It is the one reliable way to ruin the first attempt.
• Giving the answer the moment they stall. Two minutes of being stuck is not a problem to fix — it is the part where they learn.
• Correcting a mistake straight away. Let the contradiction surface: discovering a duplicate digit for yourself is worth ten reminders of the rule.
• Timing them. The site's clock only starts on the first click and exists to track your own progress, not to apply pressure. For a child, ignore it entirely.
• Playing grid after grid. Ten minutes a day beats an hour on Sunday: sudoku logic settles in through short repetition.

The rest takes care of itself. Most children go from 4×4 to 6×6 within a few weeks, and the ones who really take to it reach the 8×8 — which is not far off a real sudoku — without ever being pushed.