I love reading mysteries. Based on how many detective shows there are on TV, I would guess that most of America likes mysteries, too. So why is there so little variation in each story line?
Let's start with five examples. I cannot vouch for all of these as school appropriate because I am not familiar with them well enough to make such a call.
Hercule Poirot is a character created by the famous Agatha Christie. He's described as a vain, white, Belgian man with catlike eyes, an egg shaped head, and fabulous mustaches. He really understands human nature and solves his cases with psychology rather than tiny scraps of evidence. The endings are spectacular (may I suggest The Murder of Roger Ackroyd? Ultimate favorite!), although I do find it hard to plow through the abundance of exposition sometimes, especially when the murder takes nearly half the book to occur.
Flavia De Luce is a white schoolgirl in the 20th century in a series by Alan Bradley. She uses her outgoing (and slightly arrogant, yet lovable) nature and her love of chemistry to discover the killer of victims in her small hometown. She tells the story in a very lifelike first person, which I think sounds best in the audiobooks. I'm only halfway through book 2, but I really like this series.
Sherlock Holmes you probably know fairly well already. Sir Arthur Conan Doyle's original stories have been the object of multiple TV shows and countless allusions. He's a white, British, male who may be a little eccentric and/or arrogant at times but is extremely good at finding what others can't.
(Adrian) Monk is a character from a TV show (and apparently a book series, although I haven't read them and I don't know if the books or show came first) who uses his obsession with perfection to help solve crimes. He's a white American male who has OCD and a fear of everything unclean, so the show incorporates some humor of forcing him to act against his character.
Shawn Spencer (Psych) is a TV show character who is also white, male, and American. He has a special gift for noticing details, which he passes off as being psychic. His sense of humor (and immaturity) spices up the plot, especially with the foil between him and Detective Lassiter, the stickler to all the rules.
It seems like most detective novels and shows we have available focus around white, middle aged males in the most powerful country in the world at the time it was written. The main character has some sort of superiority complex or quirk that makes him (or the occasional her) annoying but lovable enough to keep making the writers money. An introvert is unheard of.
And it isn't just fictional detectives. It seems like we always focus on the "ideal" person in the media that fits all of the standards of society. When we make our own characters, they have to meet the standards we ourselves cannot meet. So I challenge all the writers out there- give your characters flaws. Make them awkward just to make them awkward, not to enhance your plot. How about an introverted main character? A female who doesn't have to be Hollywood skinny to be beautiful?