Sudoku Classroom

A sudoku app that teaches.

Without the techniques, a hard sudoku is just a wall. This app lays out three steps — Learn, Drill, Solve — across five course books.

■ Five books, twelve techniques

Book 1 Certain squares · Book 2 Block and line · Book 3 Sharing squares · Book 4 Rectangles and wings · Book 5 Chains. From naked single through X-Wing, Swordfish, XY-Wing and simple colouring, twelve techniques are explained one step at a time on a real board.

■ Learn → Drill → Solve

• Learn — lessons on a live board, pointing at the cell that makes the deduction work • Drill — one technique in isolation: find it, and the app grades you • Solve — a puzzle whose last gate is exactly that technique

■ Hints that reason, not just reveal

Tap Hint and it does more than fill a square. It names the technique, highlights the cells the deduction rests on, and tells you why that digit has to go there.

■ The difficulty is the technique

All 10,000 puzzles were solved through and graded by the last technique needed to finish them. These are not labels we made up. Each puzzle was verified to have exactly one solution, and every clue layout is symmetric, so the board looks settled the moment you open it.

■ Tools that help you think

• Pencil notes — place a digit and the same candidate clears itself from the neighbours • Undo — takes back exactly one move, no more • Check — tells you how many of your digits are wrong, and nothing else • 3 hearts — run out and the game simply carries on quietly, without scolding you

■ Your progress stays

Puzzles solved, time spent and score add up per book, and every single game is kept in a score history. A daily streak keeps you coming back for one puzzle a day.

■ Ads only when you ask

No banners, nothing that blocks the screen. A short video plays only when you tap to get more hints or to bring your hearts back.

■ Works offline

All 10,000 puzzles ship inside the app. iCloud keeps your iPhone and iPad in step — no account, no sign-in.

iPad is supported in both portrait and landscape. Available in English, Korean, Japanese, Chinese (Simplified), German and Spanish.