Few things pull readers out of a story and make them set the book down never to return than a story's voice that just doesn't ring true to their ears.
There are the obvious exceptions to this (SciFi, Historical, Fantasy, etc.) when the expectations are set by the genre. But in general, readers want a book that sounds like themselves.
Slang is an overused technique by many writers who are trying to gain authenticity. But the opposite usually happens. When slang becomes dated, it is one of the biggest offenders to a young reader's ears. Slang has a very short half-life and moves in and out of our vocabulary. It gives the feel that the author is trying too hard to sound cool. As an adult writing for kids, it's a huge challenge to tune ones ear to an authentic voice without dating it with slang.
Some of my favorite slang words that immediately conjure a very specific time period are:
Rad/Radical - mid-1980s
The bomb - late 1990s
I welcome you to post your all-time favorite dated words/phrases here in the comments section.
Also, check back later this week for a podcast interview with author Denise Vega who will be discussing the challenges of writing the authentic teen, male voice.