Thought of a possible improvement to the Duolingo system
Instead of just completing one section of the language tree and moving past the checkpoint to the next section, I think it would be beneficial if there was a short test after you complete the section in order to move on to the next one.
The test would include content from each lesson in the section which really assesses if you've learned everything and can comprehend the language at the skill level you're at.
If you don't pass it the first time, you know you'll need to review some stuff in that section you might have forgotten.
What do you guys think about this?
Neither one of those options really addresses what the OP is suggesting though. Those features test what you ALREADY know. OP is suggesting a review module at the end of each section that you complete that you have to "pass" before you can move forward.
The only reason I don't necessarily like it is because a) it moves back to more "traditional" language education. Moving away from the traditional approach is what makes Duolingo excellent; and b) Duolingo already makes you review older material by injecting older vocabulary into newer lessons AND by encouraging you to keep your skills gold. If you didn't pick something up the first time around, it's OK, because you're going to encounter it again.
That sounds a lot like the health system on the app. It's, well, not terribly popular 'round the forums. The skill level feature coming soon will allow a more clear indication of knowledge level in each individual skill without being mandatory to move on through the tree. I think this is much more the way to go: people can pass the skill levels in each individual skill if they want, or not.
Some trees, incidentally, aren't ordered sensibly enough for something like you propose. For instance, you'd have to have a good mastery of verbs for different animal noises before seeing something as essential for ordinary communication as the past tense in one of my trees.