This study proposes a knowledge organization facilitating human performance on scientifically relevant recall and problem-solving tasks. This organization is structured hierarchically so as to describe knowledge at different levels of detail; it is also task-adapted so that higher levels include information most important for implementing the intended tasks. The efficacy of this organization was assessed by two experiments, in experiment I, college-level subjects read a text and performed special training tasks to acquire knowledge of a physics topic organized either in the preceding hierarchical, or in a detailed single-level .organization; a third group read the single-level organization twice. In a subsequent test, subjects with the hierarchical organization performed appreciably better on tasks of recall, error correction, and knowledge modification. In experiment 2, subjects acquired knowledge in either of two alternative hierarchical organizations of the same physics topic, but with information distributed differently over the levels. As expected, in a subsequent test subjects performed better on those tasks depending on information from higher levels of their hierarchical organization. The specially designed training was effective in producing the desired organization of a subject's internal knowledge, but subjects with lower physics grades seemed less able to assimilate and use a hierarchical organization. Similar conclusions were obtained from a third experiment in which internal, knowledge organization was inferred from an analysis of free-recall protocols.