This paper presents the outcomes of a study that investigated the psychometric properties of the School Independence Measure (SIM), an assessment designed to evaluate functional performance in a school setting and to monitor changes in function over time. The SIM operationally defines and criterion references tasks essential to a child's independence at school in order to facilitate an interventions framework for setting attainable goals and for monitoring progress. The SIM builds upon the conceptual and organizational format of the WeeFIM: Functional Independence Measure for Children. The study examined the SIM and standard batteries of cognitive and behavior to establish the relationship between those processes and SIM scores. The community sample was comprised of 32 9- and 10-year old forth grade boys and girls with attention deficit hyperactivity disorder. Psychoeducational assessment data, including cognitive test scores (Wechsler Intelligence Scale for Children-III) and behavioral ratings (Conners' Parent and Teacher Rating Scales-Revised) were recorded for validity studies. Subsequently, each participating child's teacher was contacted to complete a SIM for the referred child and simultaneously for one of the child's hypothetical typical peers. Results of the study found evidence of convergent and divergent validity for the SIM and principle components analyses support the construct validity of the SIM. (Appendices include data charts.) (CR)