Conceptual knowledge is only one aspect of a good knowledge structure: how and when knowledge is activated and used are also important. We explore knowledge organization in the context of the resources model of student thinking via observations of student problem-solving behavior on a mechanics task that integrates the concepts of force, motion, and energy. We document that both introductory and advanced students may have knowledge structures with local coherences that may inhibit their access to additional useful knowledge. These results suggest that instructors and researchers need to pay increased attention to how and when students use what they know as well as to what they know.