The investigation of learning performance as an interactive function of individual differences of the learners and alternative modes of instruction is a timely topic in the area of instructional research. This research area is generally referred to as "Aptitude-Treatment-Interaction" (ATI). This paper makes some general comments about ATI efforts, with specific focus on methodological and conceptual problems connected with this type of research. In addition to providing an overview of the ATI concept, the paper discusses quantitative problems and strategies connected with this research area plus some comments about the direction ATI research may take in the future.