Hi Florence,
At the moment there's not a very easy way to view the pre vs post test scores on a per user basis.
However you can view all the quiz results for all the quizzes in a given course, int eh dashboard, go to the course, then on the left sidebar, there will be a link to the course quizzes, from there you can view all the responses (down to responses for individual questions).
I guess one issue we thought about with the post tests is that users can take these multiple times, so we'd need to determine if just their first repose should be used, or their more recent response (or an average?). So will need some thinking about as to how this type of info could be displayed in an intuitive way - any suggestions welcome!
Cheers,
Alex