School psychologists typically conduct psychological and psychoeducational assessments, provide prevention and intervention services, and consult and collaborate with allied professionals (e.g., teachers, physicians, psychiatrists, physiotherapists, occupational therapists, social workers, and nurses) and parents toward better understanding and promoting the learning and development of children and youth. Within and across these roles, school psychologists maximize their judgments by utilizing psychometrically sound instruments, recommending and using empirically based intervention programs and approaches, and making informed decisions based on theory, research, and clinical experience. The purposes of this article and this special edition of the "Canadian Journal of School Psychology" are to promote the relevance and significance of clinical reasoning in this complex process of full service delivery and highlight examples of the effective thinking and decision making undertaken by school psychologists from assessment to intervention.