There is a quote that "bad design never killed anyone," but I know that what we do is less trivial than that.
What designs have you seen cause real change or have a real influence?
Specific context behind the question:
Lord willing, I'll be giving a presentation to my wife's school for Career Day this week. I want to talk about what design is (which could be another question here, I might post later), but since I learn by example, I want to give some examples about how design makes a difference.
To answer the "what have you tried" question:
One of my favorite examples is the butterfly ballot from the USA's 2000 election...a poor ballot design probably shifted the course of my country for at least four years. but that's probably a little too partisan. Partisan concerns also knock out the comparison of health care charts - a great conversation piece about how design can be used to streamline or obfuscate data.
I love propaganda design and respect its unique place in history, but kids might not connect with that.
I could talk about the iPod and iPhone, but some of that drifts into industrial design and I think that's a bit tired of an example anyways.
I'm thinking about comparing two pieces of paper, one that has a bad font, tight leading and kerning, and is right-aligned, and one that is set a little more properly, and asking them to compare. But that's just a boring sheet of paper.