A good writer friend of mine is getting ready to run a young adult workshop on plot.  She asked if I had any tips.  My rambling (and possibly unhelpful answer) was as follows:

When I teach plot to kids I center on the definition that a story is a significant event or events that happen to someone.  I like this starting point because I can stress the key words, "significant," and "event."  The first word means that the events have to matter to some one, and the second means that something has to happen.

From there I go to Freytag's pyramid.  I know that's kind of dry sounding, but it gives them a picture of a plot as starting with an inciting moment and rising to a climax.  The pyramid is no good, though, without talking about the conflict that drives it, which for me has three parts: someone wants something, something stands in the way, and something of value is to be gained or lost.  For me, most of writing a story is about figuring out for myself what those three parts are.  Lots of times I'll start a story but I won't have a firm idea of what the three elements are, so I flounder around for a bit until I write myself to the answer.

But that's my intro to a several-week long unit.  For a workshop I might have them brainstorm what they think a story is for a while.  What they'll come up with is that a story has parts they recognize, like description, dialogue and action.  Sometimes they'll say a story has a theme (they're getting this from their lit class).  "Theme" is just a formal way to say the event is significant.  Then, because I like to get them involved in "story" right away instead of one of the other elements, like writing dialogue or creating a character, I'll have them do the seven-sentence story exercise,which really is a down and dirty mini-lesson on plot.  I have a complete description of that exercise at http://jimvanpelt.livejournal.com/81034.html.  You can see a fun and funny example of a seven-sentence story at http://jimvanpelt.livejournal.com/82058.html.  I have a series of articles specifically about plot in my  index of writing-related blog posts at http://jimvanpelt.livejournal.com/87625.html

I think that teaching plot to young adults is less about theory and more about letting them tell stories.  Every student brings their own idea of what a story is, and they have different skill levels too, so the theory part is pretty brief.  Writing stories is fun and encouraging; listening to how to write stories is pretty dull (unless you are highly motivated.).  

Teaching story writing to young adults is like teaching them how to kiss.  It's a lot more fun to practice, and they already have an idea of how to do it, than it is to sit in a classroom doing everything except kissing.  When they have problems with their stories, or they wonder why their stories aren't doing anything for their audience, then they are more willing to listen to theory, especially when it is tailored especially to the story they are working on.

By the way, the kissing lesson analogy has all kinds of weaknesses to it.  I was rushing *g*.