The rules the system runs on, without screens. Screens are in the next section on UX Designs.

1. A layer on the Path, not a section

Course Buddies is a state added to the Path a learner already uses. It is not a destination near Friends Quests, and it is not a mode you enter.

Three things follow. It is the deepest expression of self-pacing, because dropping to solo isn't exiting anywhere. It is the strongest answer to "why not modify Friends Quests," because it changes the core learning loop rather than a social tab. And it is far more buildable in one or two quarters than a new section would be.

The design tension it creates runs through every surface: co-learning has to be legible and celebratory when it's present, without making the solo Path feel broken or lesser when it isn't.

2. Six rules

These apply to everything below. Breaking one is a design failure, not a trade-off.

1. No user-generated content anywhere. Nothing a person types or records ever reaches another person. This removes the moderation surface entirely: there is nothing to report, review, or filter. It is why a quiz is a type you choose rather than questions you write, and why Nudge is a fixed action rather than a message. Speaking quizzes hold to this. No audio is transmitted; each device generates its own prompt and scores the answer locally, and what crosses between buddies is a correct answer and a pass or fail, the same as every other type.
2. No new content, and no existing content changed. Everything draws on exercises and units that already exist.
3. No new currency. Existing XP, energy, and reward systems carry the feature.
4. Additive presence only. Nothing existing is removed, moved, resized, or reserved. The layer may substitute an illustration within itself, but structure, position, content, and mechanics never change. A solo learner's experience is unchanged in every respect.
5. Clean removal. When a pair ends, its surfaces disappear and nothing shared changes shape.
6. Must read on sight. No tutorials, pop-overs, or first-run explainers anywhere. If something needs explaining, the design is wrong, not under-instructed.

3. Self-pacing is never violated

A buddy can always keep learning at their own pace. Shared moments fire when both people arrive; they never gate the person ahead. Togetherness is additive, never subtractive.

Self-pacing is close to a core Duolingo value. A feature that can stop someone fights that value and would read as not understanding the product.

4. Why the sender answers first

The learning case for Course Buddies rests on the sender doing real cognitive work. Selecting and posing questions gives the sender retrieval practice; answering gives the receiver the same. A sender who forwards auto-generated content gets no practice, and the learning claim collapses.

That requirement is met by the sender answering all five questions before the quiz sends, which is retrieval practice in the strict sense. Type selection carries intent; answering carries the learning. This is also why the confirmation screen shows the sender's score: it makes the answering visibly the point rather than an unexplained toll, and it sets up the comparison the result screen pays off.

There is no gate on correctness. A sender who gets all five wrong still sends, without comment. Gating would push people toward easy types, and it would delete the best moment in the feature: both people missing the same thing and seeing it.