A course's skill tree or language tree is the organization of the course's skills into rows representing the order of course progression.


The content of a course varies. As such some courses may contain more vocabulary and skills than others. A study published in 2012 found that one would need 34 hours of study in Duolingo to cover the first semester of Spanish in college[1][2].  




Main article: Skill

A skill is an item in the tree that consists of one or more lessons. Users must complete all the skills on each row of the tree before moving to the next row.

Bonus skill slotsEdit

Main article: Bonus skill

The language tree contains certain slots that can be filled with bonus skills.[3] These can be bought at any time provided that a learner has reached a certain point in the tree. Once the bonus skill has been purchased it remains in the tree permanently.


Main article: Lesson

A lesson in Duolingo consists of many exercises that help teach the core aspects of a skill. The lessons themselves contain various exercises.

Tree progressEdit


A Golden Owl

Typically, a learner must complete the skills in a row in order to advance to the next row of skills. As they advance through the course their fluency may also increase. Once they have finished all the skills (finished the tree), they will be awarded with a Golden Owl. However, there are shortcuts a learner may use to quickly complete the skill tree. These shortcuts include:

  • Checkpoints - Tests all knowledge of a language tree up to a certain point and once the test is completed it automatically marks all known skills as complete;
  • Placement test - Tests all knowledge of a language tree allowing learners to skip all the skills they already know; and
  • Test out - Tests all knowledge of an individual skill.

Tree updatesEdit

Tree changes
Language course contributors continually tweak and update their skill tree. The appearance of the old tree has been changed previously[4] and new lessons or skills may be added or removed to improve the learning experience.[5][6]