Abstract This study examined the effects of an assessment-based intervention plan on the appropriate classroom behavior of a socially withdrawn, Hispanic, learning disabled, third grade student. The study focused on (1) the effects of peer mediation as part of a behavioral intervention package of empirically validated components, (2) the effects of aligning assessment data to the BIP, and (3) the social validity of the assessment and intervention process. Three major strategies linked directly to assessment outcomes were worked into a behavioral intervention plan for the socially withdrawn child in the study: social skill development, self-management including positive reinforcement, and peer mediation. A single subject ABAB withdrawal design was used to evaluate the intervention. The socially withdrawn student showed immediate marked improvement in socially appropriate classroom behavior and completion of his academic work. Treatment gains maintained over time as reinforcement was thinned out. Social validity evaluation included social comparison (i.e., normative sample) and subjective evaluation by the teacher, student and peer through questionnaire data, with special consideration given to the degree of usability. ********** Social competence is essential for success in school (Kerr & Nelson, 2006; Walker, Ramsey, & Gresham, 2004). Development of social competence facilitates (1) satisfactory school performance--including teacher acceptance and adequate academic achievement, (2) positive social relationships with peers, (3) peer acceptance and friendships, and (4) the ability to adapt and cope with the demands of school environments (Marchant et al., in press; Walker, Ramsey, & Gresham, 2004). The importance of social competence has been well documented; however efforts to foster appropriate school behavior and positive social relations in students with behavioral problems have often been unsuccessful and discouraging (Gresham, Sugai, & Horner, 2001). Educators and researchers must continue to seek empirically validated interventions for increasing social competency (e.g., speaking aloud, asking and answering questions, socializing with peers) in students who lack social skills, particularly those who display internalizing behaviors (Marchant et al., in press). Students who display symptoms of anxiety, depression, and social withdrawal are typically classified as internalizers (Achenbach & Rescorla, 2001; Gresham & Kern, 2004; Merrell, Blade, Lund, & Kempf, 2003). Research has demonstrated that these symptoms have a negative influence on children's academic performance, social interaction with adults and peers, and physical health during the school-age years (Merrell & Walker, 2004; Flook, Repetti, & Ullman, 2005; Merrell, 2003,1994). However, internalizing behavioral disorders (EBD) are characterized as disturbing to the individual, rather than disturbing to others or the environment (Kauffman, 2001). Similarly, teachers often view students with internalizing behavior as merely shy, failing to recognize the ramifications of this behavior on current and future student outcomes (Marchant et al., in press). Children with internalizing behaviors are often "quiet" and "invisible"; thus they present unique challenges in referral, assessment, and intervention practices in schools. School personnel typically use "reactive" methods (e.g., office disciplinary referrals) for identifying students in need of behavioral services (Nelson, Benner, Reid, Epstein, & Currin, 2002; Walker, Cheney, Stage, & Blum, 2005). Students with internalizing problems exhibit anti-social behavior that is covert; therefore teachers identify and refer these children for needed services less often than they refer children who act out (Lane, Gresham, & O'Shaughnessy, 2002). Thus most research regarding internalizing behavior problems has focused on assessment and classification rather than intervention practices (Merrell, 2001). …