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study examined the effects of an assessment-based intervention plan on the appropriate classroom behavior of a socially withdrawn, Hispanic, learning disabled, third grade student.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strategies linked directly to assessment outcomes were worked into a behavioral intervention plan for the socially withdrawn child in the study: social skill development, self-management including positive reinforcement, and peer mediation.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 The socially withdrawn student showed immediate marked improvement in socially appropriate classroom behavior and completion of his academic work.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. (Contains 3 figures.)