Miss, me miss, me, miss, miss! :)

I think you’ve got an excellent and very clear example with your Titanic reference, so I would lead with that one. Personally I doubt the value of the Dostoyevsky example as I suspect many students will find even the strange names a barrier to understanding the point you’re trying to get across; this may be a case where our knowledge of the text could blind us to how a student will receive the information.

Yes, you must be right to suggest the point about only some of the characters being in the dark. I liked your approach including a simplified definition. Guessing you need to cater for quite a range of calibre I’d suggest something like this, incorporating perhaps two levels of definition by means of a recap, and also indicating why the technique might be valuable:


Dramatic Irony

Meaning:
The revelation to an audience of a truth that remains unrecognized by one or more of the characters in a narrative. The contrast between what the audience sees/reads and what the characters know creates an ironic tension.

Purpose:
This tension is often exploited for comic effect but is also used for darker (even tragic) contrasts of truth and falsehood. Like all tension, it assists in capturing our interest to find out how the story gets resolved.

Quick recap:
dramatic irony = situation understood by audience but not by some characters


Example 1: An Inspector Calls ~ Titanic reference (we know Birling’s statement is false, which tends to undermine our trust in any of his other beliefs and statements)

Example 2: King Lear (Act 1, sc iv) ~ when Kent has been banished by the King, he reappears to serve Lear with the words “I do profess to be no less than I seem; to serve him truly that will put me in trust…” Since we in the audience know he is far more than he seems, and yet was not trusted by the King, we see that Lear is blind to true personal worth.
http://larryavisbrown.homestead.com/files/Lear/lear_Id.htm

Example 3: I’d probably take a common example of comedy from contemporary culture (sic) such as a character played by Jim Carey in The Majestic, where we know who he is although his character has lost his memory ~ the tension in this kind of dislocation between what the character knows and what the audience knows feeds a very obviously funny string of occurrences. This humour provides the narrative drive of the story to its conclusion by resolution of the tension.
http://www.all-reviews.com/videos-4/majestic.htm

HTH! Perhaps some better examples will occur to me ~ I'll keep it jogging in mind while building a wall tomorrow :)