Can you elaborate on what you mean by it "working"? By that, I mean, what constitutes the experience being a success: the couple proceeding with the formal, official Catholic marriage? Is that the determination of success? (Or conversely, a couple who, after going through the preparation process, determine that they are ill-suited for marriage, and so break up -- would that be considered a success?)
What "works" is what I can have a conversation about with the couple.
Talk about hell usually ends the discussion.
In most cases, the couple proceed with the marriage; in a few, they decide, after much discussion, primarily using the results from the questionnaires they fill out, to break up.