Drupal Quiz Module for retake exam
You can look at the Quiz module. It also has an active Drupal Group :)


  The Quiz module provides tools for authoring and administering quizzes through Drupal. A quiz is given as a series of questions, with only one question appearing per page. Scores are then stored in the database.
  
  This module provides tools for
  
  
  Online courses (Audio and Video enabled)
  Self-learning programs
  Training programs
  Supplementary classroom activites