The lessons don't teach you all words?
Whenever one of my skills is weak and I have to strengthen I come across words I have never practised before. I can see that the words should be in the lessons but it looks like I never get them. Could this be true? Maybe the lessons phrases are based upon an algorithm that misses out on some words?
I've noticed that with a new lesson I sometimes see new words about the 3rd or 4th time I go through the lesson. Not sure if this is on purpose, or a bug, or part of an A/B test. I do recall reading recently that they were playing around with the idea of introducing fewer new words per lesson, so this may be a side effect of that.
I also see different words on the iPhone app than in the web based lesson. Again, I suspect this is a side effect of the (A/B?) re-arranging of words in lessons.
When I review the skill later I frequently see new phrases, but if memory serves, it's because I have learned new words since doing the lesson and the new phrases are more complex and incorporate the older words that "belong" to the lesson I'm reviewing plus newer words that "belong" to lessons I've done more recently.
When I do a global "Strengthen Skills" type exercise I would swear I am given words I've never seen before, but I think that's just the result of a poor memory :-/
I noticed for example that when I learn the lesson 4 for food in spanish for english there is 2 words I'm supposed to learn which never appears (cebolla and emperado). And in the words tabs they appear not only as learned but as practised today although I didn't have them when I did the lesson today.Edit I just did again the lesson 3 of animals for spanish for english and although I'm supposed to learn : pájaro, pájaros, cangrejo, araña, oso, pingüino, animales I didn't learn the first three although I did the lesson 3 times. It looks like one of the many bug of duolingo
I have got the same problem. Usually just half of the stated words are covered in the lessons. Even if I repeat the specific lesson it is always the same words coming up that were covered before but not the rest of the words of the lesson. Usually I get bombarded with these new words when I strengthen a whole set of lessons. Not sure how about others but this is not helping me to learn them. Especially if they only come up randomly and I cannot specifically target them in a lessons.
I'm learning French from English. I primarily use the ChromeOS Duolingo app. Secondarily, I use the Android app. Third, I use the web app. Each one seems to give different preference to different words. None of these methods "teach" me all the words. There are always some that are asked in a manner in which there would be no prior way to know them. So, I can confirm for you that this is absolutely happening.
For me, this is not helpful and seriously kills incentive to continue. If I want to hear words I don't know, I'll run outside and listen to French people speaking. I'm here to learn, and that is not always taking place.
I think the overall format of Duolingo is one of the best I've ever used, but oversights like these are (relatively) inexcusable. If it's an attempt at an alternative learning method, it should have been aborted before the thought made it on to paper. If it's a bug, hopefully it will be addressed (as in, publicly stated, yes, we see this bug) and fixed.