Externalizing behaviors are the most common and persistent forms of childhood problem behaviors (Campbell, 1995) and are both concurrently and prospectively related to impaired functioning in many domains (Rutter, Giller, & Hagell, 1998). Studies indicated that children and adolescents with conduct problems are at increased risk for various types of psychopathology in adulthood (Bardone, Moffitt, Caspi, Dickson, & Silva, 1996; Farrington, 1999; Fergusson, Lynskey, & Horwood, 1996; Keenan, Loeber, & Green, 1999; Moffitt, Caspi, Harrington, & Milne, 2002; Zoccolillo, 1993), delinquency (Broidy et al., 2003; Fergusson & Horwood, 2002), and impaired social functioning (Achenbach, Howell, McConaughy, & Stanger, 1998; Chassin, Pitts, & DeLucia, 1999). At the same time externalizing behaviors change so much in expression and frequency over the course of development that studies at any single time-point in development will provide only limited information or misrepresent the phenomenon (Kraemer, Yesavage, Taylor, & Kupfer, 2000). Therefore there is a growing consensus that externalizing behavior must be studied from a developmental perspective (Costello & Angold, 2000).