Here is the concept:
Student is presented with a problem. He/she may not even understand what is being asked, or may attempt.
Students reads a solution to the problem. In it there may be explanations about concepts - so there is a "content" part, but as part of an actual problem being solved, at the level the student is currently at.
If answer is correct, moves on to the next problem.
When a set of problems of a given topic is consistently correct (say 10 out of 10 consecutive questions), student is given the next topic, or the next difficulty level.
Point being: At no point is there a proper "lesson".
What are your views about such an approach, compared with lesson-solve, lesson-solve, etc.
(Thank you Joel Reyes Noche and brendansullivan07 for your comments on my previous question - I deleted it)