The Recruit

The Recruit (book 1 in the Cherub series) by Robert Muchamore

Cherub agents are highly trained, extremely talented -- and all under the age of seventeen. For official purposes, these agents do not exist. They are sent out on missions to spy on terrorists, hack into crucial documents, and gather intel on global threats - all without gadgets or weapons. It is an exceptionally dangerous job, but these agents have one major advantage: adults never suspect teens are spying on them.

James is the newest Cherub recruit. He's a bit of a troublemaker, but he's also brilliant. And Cherub needs him. James has no idea of what to expect, but he's out of options. Before he can start in the field he must first survive one hundred grueling days of basic training, where even the toughest recruits don't make it to the end...

Here's an interview with the author Robert Muchamore.