Sudoku School

Course introduction

A complete guided path from first rules to expert proof

You will learn: how the 58-lesson School turns Sudoku from trial and error into visible reasoning.

Sudoku School is the flagship learning path inside Sudoku Skills. It begins with rows, columns, boxes, and clean candidate notes, then builds toward fish, wings, Almost Locked Sets, chains, uniqueness, What-If replay, and the final Sudoku Skills Diploma badge.

The goal is not to memorize names. The goal is to see why a move is safe, practice it on a real board, and review the proof until the pattern becomes recognizable.

58 lessons cover the full beginner-to-expert course now represented in the School.
Every named technique lesson is paired with a puzzle selected to reach that technique.
Coach nudges help students get unstuck without replacing the solving experience.
Board animation lets students replay proof steps for advanced techniques instead of staring at static notes.

Teaching snapshot: The School teaches students to read candidates as evidence. Highlighted cells show the proof; red notes show what the proof removes.

How the School works

Read the lesson, solve the puzzle, then review the proof

You will learn: how each lesson uses a repeatable study loop.

Each lesson card explains what the student will learn, why the lesson fits the course, how to practice, a coach tip, what to review afterward, and what makes the puzzle interesting.

During the puzzle, the student can work independently or reveal nudges. After completion, the walkthrough and animation tools turn the solve path into a study session.

Start with intention. The lesson tells the student what idea to look for before the board begins.
Practice on the board. Students still make the moves, maintain notes, and decide when to ask for help.
Review the proof. The walkthrough explains why the key placement or cleanup was safe.
Earn progress. Badges and the final Diploma badge reward course milestones, not random solve volume.

1PrepareRead the lesson goal and coach tip.
2SolveWork the board and reveal nudges only when useful.
3ProveStudy the walkthrough, highlights, and animation frames.
4AdvanceUse the review habit in the next lesson.

Course rhythm: The School is hands-on. The app can coach, but the student builds the solving judgment.

Course map

See how the eight modules build on one another

You will learn: where each technique family lives in the 58-lesson path.

The course is organized so earlier habits make later techniques easier. Students first learn how to trust givens and candidates, then use that evidence in larger structures.

The expert modules are not isolated tricks. Fish, wings, ALS, chains, uniqueness, and What-If reasoning all reuse the same foundation: candidates, peers, links, and proof.

Module 1: Board Foundations.
Module 2: Candidate Cleanup.
Module 3: Fish Patterns.
Module 4: Wings and Almost Locked Sets.
Modules 5 to 8: Chains, uniqueness, What-If reasoning, famous puzzles, and the final Diploma badge challenge.

Teaching snapshot: The path gets more advanced, but it never stops using the same board language: cells, candidates, peers, and consequences.

Module 1

Board foundations

You will learn: how givens, rows, columns, boxes, peers, and assist colors become the language of proof.

The first module is about seeing the board clearly. Students learn what is fixed, what is still open, and how a selected cell relates to its row, column, and box.

These lessons are intentionally generous. The student should build confidence by naming evidence before entering values.

Givens are facts. They are not part of the student solve path, but they create every later restriction.
Peers create pressure. A cell is affected by its row, column, and box at the same time.
Assist colors teach attention. They help students look at the right neighborhood without changing the puzzle.
Early wins matter. Direct placements build the habit of proving, not guessing.

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Teaching snapshot: Before advanced techniques make sense, the student must be comfortable reading row, column, and box pressure around a cell.

Module 1 to 2 bridge

Candidate notes and disciplined cleanup

You will learn: why candidate notes are evidence, not clutter.

Candidate notes are the memory system for the whole School. They show what is still possible in each open cell, and they make hidden relationships visible.

Students learn to update notes after placements, avoid writing impossible values, and use candidates to compare cells and regions.

Legal candidates are values not blocked by a cell's row, column, or box.
Clean notes make singles, pairs, triples, and chains easier to see.
Bad notes create false patterns, so accuracy matters more than speed.
Every expert method later in the course depends on candidate discipline.

Teaching snapshot: Candidates are the bridge from beginner scanning to advanced proof. The student is learning how to make invisible possibilities visible.

Module 1

Naked singles and hidden singles

You will learn: the two most important placement ideas in Sudoku.

Singles are the first proof patterns students should master. A naked single proves a cell has only one legal value. A hidden single proves a value has only one possible home in a row, column, or box.

The difference matters because naked singles start from a cell, while hidden singles start from a digit looking for a home.

Naked single: this cell has only one candidate left.
Hidden single: this row, column, or box has only one place for a digit.
Review habit: ask whether the proof came from the cell or from the region.
Long-term value: many expert techniques are useful because they create new singles.

Teaching snapshot: One single is cell-based; the other is region-based. Learning the difference prepares students for every cleanup technique that follows.

Module 2

Locked candidates: pointing and claiming

You will learn: how a candidate trapped in one region can clean another region.

Locked candidates teach students to connect boxes with rows and columns. If all possible homes for a digit in a box sit on one line, that digit can be removed from the rest of the line. If a row or column confines a digit to one box, it can be removed from the rest of that box.

This is the first major cleanup idea in the School: nothing is placed yet, but the board becomes clearer.

Pointing starts inside a box and points outward into a row or column.
Claiming starts from a row or column and claims a box.
Cleanup is progress. Removing a false candidate can unlock a later single.
Student goal: name both regions involved before removing a note.

Teaching snapshot: The proof is not based on where the 6 goes yet. It is based on where the 6 cannot go outside the locked relationship.

Module 2

Pairs and triples

You will learn: how small groups of cells reserve candidates for themselves.

Pairs and triples ask students to compare a group of cells against a group of candidates. A naked pair says two cells reserve two values. A hidden pair says two values have only two possible homes. Triples extend the same idea to three cells and three values.

These lessons slow the student down in a good way: they teach how to look for structure instead of chasing the next immediate placement.

Naked sets begin with cells whose candidate lists are restricted.
Hidden sets begin with digits whose possible homes are restricted.
Triples can look messy because the three cells do not need identical notes.
Practice goal: prove the reservation before deleting outside candidates.

Teaching snapshot: The pair does not place either value immediately. It clears other cells, which is often what opens the next step.

Module 3

X-Wing, Swordfish, and Jellyfish

You will learn: how rows and columns can reserve a digit across the board.

Fish patterns are geometry lessons. For one digit, a set of rows may restrict the candidate to the same set of columns, or a set of columns may restrict the candidate to the same set of rows.

The School separates orientations so students learn the relationship, not a memorized picture. X-Wing uses two lines, Swordfish uses three, and Jellyfish uses four.

X-Wing: two rows and two columns reserve the digit.
Swordfish: three rows and three columns form the reservation.
Jellyfish: four rows and four columns create a larger version of the same proof.
Student goal: identify the base lines and cover lines before removing candidates.

Teaching snapshot: Fish are line reservations. Once the digit is reserved inside the pattern, matching outside candidates in the cover lines can be removed.

Module 3

Finned and sashimi fish

You will learn: how imperfect fish patterns still produce safe eliminations.

Real puzzles often do not present perfect textbook fish. Finned and sashimi patterns teach students how one extra candidate or one missing corner changes the proof without making it random.

These lessons are important because they keep fish logic practical. Students learn to ask what the fin can affect and why the elimination must see the fin area.

Finned fish add one or more extra candidates near the fish body.
Sashimi fish are almost fish patterns with a weakened corner.
The fin matters. The target must be placed where both the fish body and the fin logic can see it.
Practice goal: separate the fish body from the fin before trusting the cleanup.

Teaching snapshot: The lesson is not just to spot a fish shape. The student learns why the fin narrows the safe cleanup area.

Module 4

XY-Wing, XYZ-Wing, and WXYZ-Wing

You will learn: how a small group of candidate cells can force a shared cleanup.

Wing techniques are compact conditional proofs. A pivot or shared group creates two possible paths, and both paths force the same candidate into a wing cell. Any outside cell that sees the forced homes loses that candidate.

The School uses animation here because wing logic is easier to understand when the branches are played one at a time.

XY-Wing uses three bivalue cells.
XYZ-Wing adds a pivot that can also hold the cleanup digit.
WXYZ-Wing expands the same idea to a larger candidate group.
Student goal: identify the pivot, wings, shared candidate, and cleanup target.

Teaching snapshot: Wings are small but powerful. The target loses 3 because it sees both possible homes for the forced 3.

Module 4

Almost Locked Sets: ALS-XZ and ALS-XY-Wing

You will learn: how groups that are one candidate short can force eliminations.

An Almost Locked Set has one more candidate than cells. If one candidate is removed or restricted, the set becomes locked. ALS techniques use that pressure between two or three sets.

The School gives ALS-XZ and ALS-XY-Wing dedicated animation steps because the branch logic is the lesson: one route forces the shared candidate in one set, and the other route forces it in another set.

ALS-XZ links two Almost Locked Sets with a restricted common.
ALS-XY-Wing uses two restricted commons through a bridge ALS.
Shared candidates are removed from outside cells that see every possible home.
Student goal: read the ALS cells first, then watch how the restricted common creates the cleanup.

Teaching snapshot: ALS lessons are about group pressure. The set is almost locked, and the restricted common decides how the shared cleanup candidate must behave.

Module 5

Skyscraper, 2-String Kite, and Turbot Fish

You will learn: how one digit can travel through strong links.

Single-digit chains teach students to follow one candidate through alternating possibilities. If a digit has only two homes in a unit, one of those homes must be true. Chaining those choices can prove a cleanup elsewhere.

These lessons prepare students for coloring, X-Chains, and more advanced AIC reasoning.

Skyscraper connects two rows or columns through offset strong links.
2-String Kite links one row and one column through a box.
Turbot Fish is a compact strong-link chain with a cleanup target.
Practice goal: trace the endpoints and confirm the target sees both possible truths.

Teaching snapshot: The target loses 7 because either endpoint path puts 7 where the target can see it.

Module 5

Simple Coloring and X-Chains

You will learn: how alternating truth colors turn a single digit into proof.

Coloring gives students a visual way to reason about one candidate. Opposite colors represent opposite possibilities. If a target sees both colors, it cannot contain the candidate. If one color contradicts itself, the other color must be true.

X-Chains extend this idea into longer alternating-link paths for one digit.

Color traps remove a candidate from a cell that sees both colors.
Color conflicts prove one color false when two same-color cells see each other.
X-Chains use alternating strong and weak links for one digit.
Student goal: follow the chain slowly and explain the endpoint before deleting the target.

Teaching snapshot: The red 4 is not part of the chain. It is removed because it sees both possible colors.

Module 6

XY-Chains, Remote Pairs, and AIC / Grouped Chains

You will learn: how proof can move across multiple digits and grouped links.

Multi-digit chains are expert proof paths. Instead of following one candidate, the student follows implications between candidates and cells. XY-Chains use bivalue cells, Remote Pairs repeat the same pair through a chain, and AIC / Grouped Chains can include grouped endpoints.

The School keeps these lessons bounded and visible. Students should learn the proof path, not feel lost inside an arbitrary search.

XY-Chain follows bivalue cells until an endpoint cleanup is forced.
Remote Pairs use repeated two-candidate cells to prove an outside removal.
AIC / Grouped Chain combines alternating inferences with visible proof metadata.
Student goal: read the chain as if-then links, one step at a time.

Teaching snapshot: The value changes along the chain, but the proof still ends with a target that sees both dangerous endpoints.

Module 6

Forcing chains

You will learn: how controlled branches can prove a placement or removal.

Forcing chains are disciplined branch proofs. The student tests a candidate or value and follows only forced consequences. If every route reaches the same conclusion, that conclusion is safe. If a route contradicts the puzzle, the starting assumption is false.

This module is the bridge between normal chain reading and the School's What-If training.

Placement proof: multiple branches all force the same value into a cell.
Elimination proof: a candidate leads to contradiction or all paths rule it out.
Bounded reasoning: the School keeps the chain readable and reviewable.
Student goal: separate disciplined proof from guessing by naming what each branch proves.

Teaching snapshot: A forcing chain should feel like a short proof tree, not a guess. The branch is useful only because the consequences are explained.

Module 6

Unique Rectangle and BUG+1

You will learn: how the one-solution promise creates expert-level clues.

Uniqueness techniques use a special assumption: a proper Sudoku puzzle has exactly one solution. Unique Rectangle prevents a deadly two-solution pattern. BUG+1 identifies the one cell that breaks an otherwise balanced bivalue grid.

The School calls out this assumption clearly so students understand why uniqueness methods are different from ordinary candidate logic.

Unique Rectangle removes a candidate that would leave an ambiguous rectangle.
BUG+1 finds the extra candidate in a board that is otherwise made of bivalue cells.
Assumption matters. These lessons rely on the puzzle having a unique solution.
Practice goal: state the uniqueness risk before applying the cleanup.

Teaching snapshot: The danger is not just one cell. It is the rectangle pattern that could allow two interchangeable solutions if the extra candidate were ignored.

Modules 7 and 8

What-If replay, famous puzzles, and the Diploma badge challenge

You will learn: how expert students review branches, contradictions, and complete solve paths.

The final modules turn advanced solving into reflective practice. Students learn to save a decision point, test a branch, understand why it fails or succeeds, and return with proof.

The famous-puzzle lessons and final badge challenge are not just victory laps. They ask students to combine techniques, stay organized, and use the walkthrough as a study tool after the solve.

Cube-combination branching shows how a hard puzzle can require a controlled decision point.
What-If replay lets students explore a branch and rewind with an explanation.
Famous puzzles demonstrate how advanced techniques cooperate in a real solve path.
Sudoku Skills Diploma badge marks completion of the full School inside the app. It is a fun achievement badge, not a formal certificate or credential.

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Teaching snapshot: The branch point is valuable because the student can study it. A wrong path is not wasted if it teaches why the successful path is forced.

Next lesson

Introduction to the art of solving Sudoku

A complete guided path from first rules to expert proof

Read the lesson, solve the puzzle, then review the proof

See how the eight modules build on one another

Board foundations

Candidate notes and disciplined cleanup

Naked singles and hidden singles

Locked candidates: pointing and claiming

Pairs and triples

X-Wing, Swordfish, and Jellyfish

Finned and sashimi fish

XY-Wing, XYZ-Wing, and WXYZ-Wing

Almost Locked Sets: ALS-XZ and ALS-XY-Wing

Skyscraper, 2-String Kite, and Turbot Fish

Simple Coloring and X-Chains

XY-Chains, Remote Pairs, and AIC / Grouped Chains

Forcing chains

Unique Rectangle and BUG+1

What-If replay, famous puzzles, and the Diploma badge challenge