Would it be possible for you to make a vocabulary list for all lessons as an attachment like the grammar instructions? That would be a nice overview and would definitely help people to focus on the vocabulary of that specific lesson. After a lesson you could directly check which words you remembered or had difficulties with. Or even the users would know how much they've already learnt, or sometimes even work with other people for example in order to be asked just the words etc.
Best regards Floriboman
Here is the trick in the first post: https://forum.duolingo.com/comment/16433350/Word-lists-for-what-we-ve-learned