Questions related to learning by strengthening or practicing are answered below.
Strengthen skills

How does general strengthen skills work? Edit

The Strengthen Skills button on the home page allows you to practice the student's weakest individual words and concepts, but won't necessarily strengthen a particular skill, since the words may come from many different skills.[1]

How does the Strengthen skill button within a skill work? Edit

Practice skill button will target that skill specifically".[1]

How is the XP reward calculated? Edit

According to Luis von Ahn:[2]

The idea is that the number of XP you earn now depends on how weak the words are in the lesson. Lessons in which all the words are already at maximal strength will only give you 3 XP, and lessons in which all words are at minimal strength will give 10 XP. 

How much practice does it take to strengthen words/skills/courses? Edit

All words practiced
Duolingo often experiments with the algorithm so this is subject to change. As of 01 September 2014, "words are strengthened every time users practice them".[2]  For example,  a skill with with 50 weak words may require more than 5 skill specific practice rounds (general strengthen skill may take far longer), and a whole tree more than 50 rounds.  

How can I practice what I've learned? Edit

Users can practice skills using Flashcards and by using tools for practicing.

How do I keep my tree golden? Edit

A tree is kept golden by regular practice. There are some strategies that can be followed to achieve this.[3][1]

What happened to duels? Edit

According Duolingo staff, Duels was removed because "with Duels, and the tab bar at the bottom of iOS, people were quitting Duolingo quicker than they would have been without those features around, and these were taking up prime real estate for other things we'd like to try (like a permanent Coach bar)".[4]

Can more than one skill be strengthened? Edit

Yes, it is possible to strengthen more than one skill if words from those skills appear in a practice session.[5]

Can I complete a strengthen session without improving skill strength? Edit

Yes, it is possible to complete a practice session without a 'visible' improvement to the skill strength. However, the words' strength may still be improved.[5]

Does a failed practice session improve word/skill strength? Edit

It depends, timed practice may improve the skill/word strength even if the user fails it.[1]

How does Duolingo choose words for practice? Edit

Duolingo chooses words using a spaced repetition algorithm.

How does skill/word strength work? Edit

Skill strength is a measure of users' proficiency with a particular skill. It is affected[1] by accuracy, peeking, practice frequency, time, and other metrics.[6]


  1. 1.0 1.1 1.2 1.3 1.4 Notice some changes in word strength?
  3. Greg's Reflections: How to Make a Gold Duolingo Tree
  4. Staff member tylrmurphy comment on An update on anything?
  5. 5.0 5.1$comment_id=4089599
  6. What happens when you peek?