A lesson is the core unit of Tarc's learning path — a short, focused session mixing new material with review.
Each lesson presents a sequence of steps: teaching screens that introduce new content, and quiz steps that test it, followed by a results screen showing what you got right and any XP/gems earned. A progress bar at the top of the lesson screen tracks how far through the current lesson you are.
Correct answers contribute to your XP, gems, and the "words read" and "correct answers" counters used by achievements. A perfectly completed lesson (no incorrect answers) counts toward the "Perfectionist" daily quest and related achievements.
Lessons aren't purely linear — previously learned material is scheduled back into later lessons based on how likely you are to have forgotten it, rather than on a fixed repeating cycle. For the Arabic Starter course specifically, this scheduling is handled by Tarc's newer lesson engine (internally called Engine2); all other course levels use the original lesson system. Both produce the same lesson experience from your perspective.
Outside the main lesson path, the Practice tab offers standalone modes — vocabulary drills, listening exercises, and matching games — for extra reinforcement. These don't advance your course level but do count toward XP, gems, and relevant quests/achievements.
A close button in the lesson screen lets you exit before finishing — progress made up to that point (XP/gems already earned for completed steps) is kept, but the lesson itself isn't marked complete until you finish it.
XP and gems already earned from steps you completed are kept, but the lesson itself isn't marked as finished until you complete it.
Completing a lesson with no incorrect answers — this counts toward the Perfectionist quest and related achievements.
They contribute to XP, gems, and relevant quests/achievements, but don't advance your position on the course's learning path — only main-path lessons do that.
The review scheduling behavior is the same from a learner's perspective; internally, the Arabic Starter level uses Tarc's newer lesson engine while other levels use the original system, but both apply the same spaced-review principle.