I recently did a mashup of Monsters and Other Childish Things and Bubble Gumshoe. It's a pretty excellent combination.
The thing that I really liked about it is that it allows you to do a little bit of magic into Bubble Gumshoe, without needing to make the PCs too powerful, or changing the economy, and highschool is a good place for Monsters and Other Childish Things, since, I find that playing 10 year olds with adults can be a little hard. Meanwhile it's good because you can have not-empowered PCs who are trying to solve problems, while the monsters can come in as the thing for the action/conflict scenes.
For my hack, I just had the PCs build a monster, and then not build a kid. And then build a Bubble Gumshoe character. And then, the PCs had both. Let the characters have relationships to allow the monsters to get hurt - but it's not going to be a big deal.
For dice, players use d6s and Gumshoe mechanics, they are normal people. Monsters use d10s and ORE mechanics, they are using non-platonic geometry.
For villains - I just made witches and other cultist, and just game them normal Gumshoe stats on them, but also gave them "magic" which was basically just ORE skills, and I allowed them to affect monsters. I got to have the line "I will summon Yog-Sothoth, and he's going to eat the rich" - which was just a lot of fun!
So - yeah - basically - if you want to run a nice urban fantasy young sleuth game, Monsters and Other Childish Things and Bubble Gumshoe smashup together real well!