Suggestion: Changing the coins system
Coins are an excellent way to motivate in the beginning, as they multiply quite quickly and your language level goes up. The language level, is supposed to show how well do you know the language, but I fear that it is not the best estimate. What happens is that for every task you complete, you gain roughly 10 coins, whether you learned a lot from the experience or not much. As I see it, the language level is proportionate to the total amount of time you have spent so far on Duolingo rather than how good you are.
I suggest the following alternative: There already exists a very good algorithm for assesing one's word strength. Each word has 4 bars. Let's say the 1st bar is worth 1 point, the 2nd worth 2 points, the third - 3 and the 4th - 4 points. that way you have a total of 10 points available for each word. As the words' strength decay over time, so does your points.
Using this alternative, for every lesson you complete, the amount of points you would get will be somewhat proportionate to how much you've learned. Also, you would get a very good incentive to continue learning, and also to go back and refresh words you haven't seen in some time,
I would be very happy to hear your feedback
Lessons get harder as you progress, don't worry. I found that on my first day, I made tremendous progress, earning coins, but later on I had to fight to get lessons finished in a half an hour. Which means that in 2 hours I might only get 40 coins! Whereas practicing previous material earns coins much more quickly, but you don't actually learn anything new.
I think that obviously the coins do not reflect mastery, but neither do vocabulary lists. For example, someone could have a great vocabulary, but poor listening comprehension, or bad grammar when translating. Verb conjugation is a very important skill only gained through practicing the verbs in all kinds of situations. The present system works because it rewards you for doing all kinds of activity- translation, listening, learning grammar, practicing, and learning vocabulary. Not just vocabulary.
And I think you are assuming that it is possible not learn by doing exercises. If the exercises were multiple choice grammar, I would of course agree. But the way that the questions work now, I think that any kind of progress on the tree reflects learning, since it means that you either already possessed the knowledge necessary to have 80% correct, or you learned them through the course.
Thank you Adrian for you feedback.
But I think that what you're saying only strengthens my point. You said that: "in 2 hours I might only get 40 coins! Whereas practicing previous material earns coins much more quickly", This means that learning new skills isn't worthwhile (from a competitive point of view), and it's better just redoing basic lessons. and also: "any kind of progress on the tree reflects learning" Keep in mind that progress on the tree, which is done by "all kinds of activity- translation, listening, learning grammar, practicing, and learning vocabulary." translates DIRECTLY into word strength. What I mean is that your overall word strength doesn't just reflect your vocabulary, it reflects your progress on the tree, which reflects mastery.
I just presented the basic idea, but it could be a more advanced algorithm. For example it's possible to assign different weights to different words. As the lessons get harder, the words learned in those lessons could be worth more than the more basic words.
Think of the following example: Someone started using Duolingo a year ago, got about 600 coins, then did a long break and returned a month ago. He still has the same amount of coins, but definitely knows much less. As he needs to refresh basically everything, starting from Basics 1, and redo all tree progress. By the time he finishes redoing everything he ends up having 1200 coins, whereas using the method I presented he would have the same exact amount of points (or maybe a bit more if new words were presented) from this point on the lessons get harder and these 600 extra points would normally reflect a much higher level of mastery