This dissertation reports efforts to develop instructional materials on linear momentum, angular momentum, and forces on rigid bodies in standard introductory physics course. Many common errors in understanding of physics concepts are described. Some of these have been previously reported. Other cases represent new instances of common patterns of student reasoning, notably the conflation of related concepts. In cases where persistent student errors were already well known, tutorial instructional materials existed at the start of this project. These materials had been developed with specific student difficulties in mind, but in some cases, were less effective than was hoped. Through further exploration into student thinking by analysis of responses to written and online questions, individual student interviews, and classroom interactions, we improved our understanding of students' conceptual errors. We also identified several specific cases on which students appeared to hinge naturally their understanding of a concept or principle. For some students in some situations, invocation of one of these cases as support for a principle appears to be relatively spontaneous; however, in most cases, students may think more productively when guided to consider the case and assign it a pivotal role. Thus, in the final design, the instructional strategies of the tutorials are intended to promote naturally productive paths of student thinking. In this dissertation, we report on the observations and reflections that drove the instructional development and demonstrate the increased effectiveness of the instruction.