Most products teach something, whether or not anyone on the team calls it teaching. Onboarding, tutorials, docs, empty states, the order features unlock, the defaults that hold a novice's hand — all of it is a curriculum, usually one nobody designed. This skill covers the three decisions that make it work: what goes in, in what order, and with how much support — plus the decision teams skip, which is how the support comes off.
Duolingo is the case study because it has published unusually candid accounts of these choices, including the A/B results that cut against its own preferences. Your product is the target. Nothing here is about language learning.
Boundary. This skill owns where a thing sits in the path and what scaffolding surrounds it. Whether a rule gets stated at all, and in what compressed form, belongs to the rules-and-heuristics skill — sequencing and explaining get conflated constantly, so keep them apart.
Scan the descriptions and follow only the [[wikilinks]] you need.
What goes in, and in what order
- [[references/sequence-by-task-not-by-taxonomy]] — the expert's structural order is the wrong first order; teach each primitive at the moment a real task needs it.
- [[references/rank-what-you-teach-by-cost-of-getting-it-wrong]] — sort by consequence, not completeness, and publish the list of errors that are safe to keep.
- [[references/sequence-by-frequency-and-declare-the-tail-optional]] — derive the head from a real corpus, then tell users out loud that the tail is optional.
- [[references/borrow-an-external-standard-as-the-spine]] — invented levels are unfalsifiable; a borrowed standard gives you a bar you cannot quietly move.
- [[references/front-load-the-context-a-later-rule-will-need]] — plant cheap material early so a hard concept can be induced from examples rather than asserted.
Support, and how it comes off
- [[references/scaffold-and-fade-on-a-schedule]] — support starts high and decays on a schedule you wrote before shipping; the fade is the design.
- [[references/make-the-scaffold-removable-by-the-user]] — a visible off switch beats a guessed threshold, and many users will never flip it.
- [[references/the-crutch-that-makes-you-cheap-to-build]] — the scaffold that makes content cheap to author is often the one preventing the skill from forming.
Practice that actually transfers
- [[references/recognition-then-guided-then-production]] — pick, then copy a worked example, then produce unaided, all inside one session.
- [[references/do-the-real-thing-badly-on-day-one]] — put the crude version of the target behaviour in the first session; the one real exception is perception before production.
- [[references/train-the-shared-bottleneck-where-it-is-cheapest]] — when two skills stall on the same resource, drill it in whichever context costs least.
Honesty about coverage
- [[references/pick-one-variant-and-name-the-choice]] — teach one default, accept the alternatives as correct, and say that you chose.
- [[references/structured-coverage-catches-what-use-never-surfaces]] — usage is distributed by frequency, so a gap presents as the absence of an experience.
Sibling skills
- [[../duo-gamification/SKILL]] — progression that is felt: XP, levels, difficulty ramps. This skill decides the content of each stage; that one decides how reaching it feels.
- [[../duo-product/SKILL]] — ruthless prioritization and raising the bar, applied to the product rather than to the path through it.
- [[../duo-experimentation/SKILL]] — every ordering claim here is testable, and Duolingo's own A/B data contradicts one of them.
- [[../duo-retention/SKILL]] — a curriculum nobody returns to teaches nothing; the habit loop is the precondition for all of this.
Sources
Thirty-four posts from blog.duolingo.com (crawled 2026-09-22), covering course construction, CEFR alignment, scaffolding and exercise design, pronunciation and grammar prioritization, dialect and variant choices, and the Math and Chess courses. Each node carries its own dated citations.