The purpose of this study was to develop standardization data for the Functional Assessment Intervention Program (FAIP; University of Utah, Utah State University, & Utah State Office of Education, 1999), a computerized, functional behavioral assessment expert system. Reliability, validity, and utility analyses were conducted with students serving in either regular or special education classrooms who were rated by their teachers as having externalizing problematic behaviors. Results suggest that the FAIP demonstrated evidence of good interrater agreement and test-retest reliability for both behavior function and overall agreement. The FAIP also shows evidence of concurrent validity when identified behavior functions are compared to behavior functions identified on the Motivational Assessment Scale (MAS; Durand & Crimmins, 1992) and the Functional Assessment Interview (FAI; O'Neill et al., 1997). Most users preferred the FAIP to the two other functional assessments (MAS and FAI), ranking it higher overall and on an item-by-item basis. Implications for school psychologists using the FAIP with students who exhibit externalizing behavior disorders are discussed.