Tasks are essential in fostering students' learning processes, and thinking skills are considered to be of central importance to learning. In order to analyse how tasks promote the development of thinking skills in school geography, we need an instrument that looks beyond a simple distinction between lower and higher order thinking. It should be able to identify types of tasks based on distinctive elements on the way to acquiring powerful knowledge or knowledge of high epistemic quality. In this paper, we describe the development of an instrument based on the adaptation of existing categorisations and the use of Bernstein's recognition and realisation rules. The instrument distinguishes five levels of thinking: lower order thinking, use of thinking strategies, parts of higher order thinking, higher order thinking, and reflection. The instrument was employed to analyse tasks in geography textbooks used in the Netherlands and the German State North Rhine-Westphalia, with researchers and teacher educators in both states considering its efficacy both plausible and practicable. The results show that the instrument is sufficiently sensitive to identify differences in types of tasks and the extent to which access to powerful knowledge is fostered.