Several researchers have suggested the importance of being responsive to students' needs in research supervision. Adapting support strategies to students' needs in light of the goals of a task is referred to as "adaptivity." In the present study, the practice of adaptivity is explored by interviewing expert thesis supervisors about diagnosing student characteristics in order to determine students' needs and concurrent adaptive support strategies. The findings suggest that next to competence, supervisors also diagnose elements of students' determination and context. With respect to support strategies, it is suggested that supervisors adapt to student needs in terms of explicating standards, quality or consequences, division of responsibilities, providing more/less critical feedback and sympathising. The complexity of the relationship between diagnosing student characteristics and adapting support strategies is illustrated and needs further study.