Determination of the cognitive and behavioural demands of work is an important part of holistic workplace intervention. Attention to these factors is especially important when developing return-to-work programs for persons with reduced cognitive, behavioural or psycho-emotional capacity, and when designing risk management programs in organizations. Occupational therapists have the background knowledge and skills to assess these components of work, but often lack valid and reliable measurement tools. This paper reports on three field studies that assessed the reliability and validity of ratings made by novice users of the City of Toronto Job Demands Analysis, which includes a measure of cognitive and behavioural work demands. Numerous challenges to accuracy and reliability that are common to empirical measurement were disclosed, including the necessity for clear and strong definitions, and the importance of thorough rater training. Implications for therapist training and mentorship are discussed.