Jan, I can't resist an education / school issue!  I'm no expert, so take it for what it's worth......But to start, I would think about which audience I was more familiar with, either 4th graders or high school kids.  The better you know your audience, the better you can appeal to their senses of short-term thinking, long-term thinking, wants, needs, desires, and hopes for the future.  Each audience has a different perception of their own reality, and likewise, they each have different prior knowledge regarding science and the concept of a career.  If you brought all of these variables together into an exciting, informative, and encouraging format, a science career could nearly sell itself.  What I've just said is a mouthful, so I know it may take time to chew on.  You have to try and make their hair stand straight up in the first sentence or two, and from then on, just keep pouring on the juice.  Easier said than done!