For my master's in computing science, I am currently following two courses which largely consist of presentations given by the students themselves. The idea is that students research one topic in-depth, and learn about the other topics from others.
I've attended four such presentations today. One was quite good, one was mediocre and two were downright embarrassing. In view of my past experiences with such presentations, I found this a decent score.
Why doesn't this system work?
Firstly, students often don't know the material well enough. The presentation can then go one of two ways. Either the material that is not understood is skimmed over, or it is left out. If the hard stuff is only skimmed, we see slides with many complicated formulas, algorithms, graphs and numbers, but the presenter hardly touches upon them. Upon asking a question to dig up more information, only stutters come out. Equally bad, if the hard stuff is completely left out, we end up with a presentation so shallow that it is nearly without content. When we ask more detail, it turns out that the presenter knows no more than he told.
Secondly, most people cannot teach. Understandable, because teaching and explaining is hard. Why else would teachers have to go through years of training before they are allowed in front of a full classroom? And even then, most teachers are mediocre. University professors, despite knowing their subject very well, have received hardly any training at all, and are usually worse. Therefore students cannot be expected to be able to explain something properly. Those who can are the exception, not the rule.
It is already hard enough to get complicated material into your own mind. To get it into someone else's is much, much harder. Forcing people to attempt both at the same time is a recipe for failure.