The transition to school is seen as an extensive process of adaptation during which children need to adjust to school standards. Successful adaptation is reflected in children's classroom behavior (i.e., prosocial behavior rather than behavior problems) and academic performance (Petriwskyj, Thorpe, & Tayler, 2005). It is well documented that cognitive abilities (i.e., IQ) are linked to academic indicators of success in school (e.g.,Deary, Strand, Smith, & Fernandes, 2007). Recently, however,Duckworth and Seligman (2005)presented evidence that the ability to self-regulate has greater influence on a student's academic performance than his or her IQ. Self-regulation (the motivation and ability to control one's emotions and behaviors in potentially stressful situations) affects children's ability to adapt to and learn in formal school settings (Trommsdorff, in press). In this study, we refer to self-regulatory skills such as delaying gratification, following instructions, and inhibiting impulsive or aggressive behavior asbehavior regulation(Kopp, 1982). The development of behavior regulation is influenced by the family environment (Calkins & Howse, 2004; Suchodoletz, Trommsdorff, & Heikamp, submitted for publication). As a result, significant differences in behavior regulation exist among children when they enter formal schooling among other things (McClelland et al., 2007; Ponitz et al., 2008). Deficits in behavior regulation may cause social and academic adjustment difficulties in school (Calkins & Howse, 2004; Eisenberg et al., 2000; McClelland, Morrison, & Holmes, 2000). Therefore, it is important to understand the function of behavior regulation during the transition process.