An international trend in school psychology services is a shift from an emphasis on assessment-based activities to a paradigm of consultation problem-solving and behavioural intervention. As the profession experiences an expansion of roles and functions, school psychologists should have an understanding of a critical aspect of behaviour change: "treatment integrity" (Gresham, 1989). Treatment integrity (or fidelity) refers to the extent to which an intervention is implemented as intended (or planned). This article describes the construct of treatment integrity as it relates to the implementation of consultation-derived behaviour intervention plans. Practical approaches for assessing and monitoring the integrity of treatments are presented. A treatment-monitoring interview (TMI) is proposed as an initial step towards developing a technology to assess and facilitate treatment integrity in school-based behavioural consultation practice. Limitations, implications for practice and future research directions are discussed. (Contains 2 tables.)