Background: School refusal behavior is a particularly nettlesome problem for mental health and education professionals because of its symptom severity and heterogeneity as well as lack of consensus regarding inclusive classification strategies. Alternatively, a functional model of school refusal behavior may provide a particularly useful way of organizing, assessing, and treating this population. Method: The present study included 222 youths aged 5-17 years (134 males, 88 females) with school refusal behavior and their parents. Participants were assessed at a specialized university-based clinic for youths with school refusal behavior. Child self-report and parent-based measures of forms of behavior related to school refusal as well as functions of school refusal behavior were employed. Results: Hierarchical regression analysis and structural equation modeling revealed that function was a better determinant of degree of school absenteeism than behavior form. Conclusions: Assessing the function of school refusal behavior is likely a key factor in the evaluation of this population and may be linked to informed decisions about choice of treatment.