When you write a "smart" character, what does that mean? How do we define "smart?"
Writers often fall back on the idea of the "genius" character -- a character with a ridiculously high IQ who can solve any puzzle and store libraries of data inside their skull. They're the characters who are years ahead of the rest of their peers in book knowledge, but are still taking Algebra and basic English for some bizarre reason. You know... "Mr. Collins was talking about Shakespeare, so I tuned out. I'd already read Shakespeare's entire body of work in the fifth grade. I needed to focus on figuring out the cypher so I could help my love interest build a rocket ship to the moon later."
It seems "intelligence" is often confused with "knows a bunch of facts and stuff." This isn't necessarily true. A character can know LOTS of things and still be a fool. Knowledge and applied knowledge are not the same thing. It's no good to have a character who's incredibly well-read and already took honors biology if there's no real applied use for that knowledge beyond proving that they're a smarty-pants. So they know how to divide by zero. So what? How does that enrich the character?
Just like writing a character who's too perfect, writing a character who's too uniformly and stereotypically intelligent stretches the boundaries of belief and often becomes tiresome. Which is not to say that teenage characters can't or shouldn't be smart. I very much approve of intelligent teen characters. I write them. However, just as it isn't realistic for someone to be beautiful AND a sports whiz AND valedictorian AND a musical prodigy AND the center of the social scene, it's not realistic for a person to be intelligent in all possible areas.
This is where the Theory of Multiple Intelligences comes in. If you'd like to read about it in depth, here's the Wikipedia entry. In a nutshell, the theory suggests that people are intelligent in different areas of cognitive ability, and that excelling in one area doesn't necessarily mean someone is more or less intelligent than someone who excels in a different area. It's basically exactly what it sounds like: the theory that you can be different kinds of "smart."
It's extraordinarily rare (maybe impossible) for someone's brain to function at optimal intelligence in every possible area. Someone who's brilliant at math might be crap at communication skills. A gifted public speaker may be be very perceptive when it comes to other people, but terrible at understanding themselves. This sort of thing also applies to the variety of ways we learn. Some of us learn better by doing, others by watching, and still others by listening.
The Theory of Multiple Intelligences lists some particular areas of intelligence -- logical-mathmatical, spatial, linguistic, bodily-kinesthetic, musical, interpersonal, intrapersonal, naturalistic. We see some of this already in stereotypical characters, like the nerd who's really good at science but really bad at anything physical. However, there are even more areas of intelligence to consider. Emotional intelligence -- the ability to understand people and gauge their emotional responses appropriately, similar to empathy. The ability to think abstractly about situations, approaching from a different angle to see what others missed. "Common sense." One could even argue for extrasensory intelligence -- the ability to perceive things beyond the normal human senses.
This approach to intelligence is important for character development because it makes you really consider where your character is strong and where they're weak. This humanizes the character, making them more relateable and believable. It also creates built-in conflict. If your character is really good at logic but really bad at social interaction, how does that play out in the story? If they have a knack for understanding people but very poor empathy/emotional intelligence, what does that mean? (It means they're Sherlock Holmes, is what that means).
Consider your super-duper smart character again. Where do they excel? What is the opposing quality to that? Don't go for the easy out (again, stereotypical science geek who's bad at sports). If they're really intelligent in one area, where can they falter that will make for the most conflict in the story? Stop thinking of intelligence as only book smarts and start thinking of the other ways people display intellect. As with anything in characterization, it's all about striking the right balance.
When you think of a "smart" character, who do you think of, and why? Do you feel that they're balanced?