In this chapter research relating to school mathematics is used as an instance to critique commonly used methods and instruments employed in educational research to determine performance and single or multiple aspects of affect. Advances in technology that have enabled the adaption of previously used instruments are described. Self-report measures, administered face-to-face and on-line, and real-time and virtual observational methods are discussed in some detail. Illustrative data from specific studies are provided. Interpreting the different measurement outcomes is, it is argued, far from unproblematic. This discussion raises issues relevant to research in a range of paradigms but is particularly pertinent to educational research conducted in the neo-positivist paradigm.