School refusal behavior is a common problem seen by mental health professionals and by educators but little consensus is available as to its classification, assessment, and treatment. This study assessed 143 youth with primary school refusal behavior and their parents to examine diagnoses that are most commonly associated with proposed functions of school refusal behavior. As expected, results indicated that great heterogeneity in diagnoses marks this population. In general, anxiety-related diagnoses were associated more with negatively reinforced school refusal behavior; separation anxiety disorder was associated more with attention-seeking behavior; and oppositional defiant disorder and conduct disorder were associated more with pursuit of tangible reinforcement outside of school. These results are discussed within the context of classification, assessment, and treatment of this population.