Well, I have to say that it is not my idea. I was at the Macmillan seminar in Moscow on February 1 where one of the speakers was Sam McCarter, the author of Ready for IELTS. 

Among other things he suggested an interesting activity aimed at helping students organize their thoughts in the context of a written exam preparation.

Students write a draft of the essay. Then they write THE SUMMARY OF WHAT THEY HAVE WRITTEN in their essays. The summary is given to another student to read. This student will have to say, judging by the summary, what the original written text is about and what ideas are argued there. Many students find, to their surprise, that when their classmates read summaries, their interpretations are very different from the original text. The wider the gap, the more disorganized (or illogical) is the original text.

The essay can be considered logical and clear if other students are able to understand the main ideas from the summary.