A challenge for urban systemic reform initiatives in science education has been to achieve local, state, and national standards for teaching and learning. We have collaborated with teachers in the Detroit Public School System to design project-based curriculum materials that contextualize the learning of science in meaningful real-world problems, engage students in science inquiry, and use learning technologies. We present a sixth grade project-based science unit in which students explored the driving question “How Do Machines Help Me Build Big Things?” and address the science learning goals of balanced and unbalanced forces, simple and complex machines, and mechanical advantage. Twenty-four teachers and over 2500 students in Detroit participated in enactments of this project over 4 years. Student learning outcomes were determined for the three learning goals and inquiry process skills using pre- and postachievement tests. Achievement outcomes as measured by the pre/posttest show significant and consistently high learning gains, even as participation in the project increased to include greater numbers of teachers and students in successive enactments, and leadership of the professional development support for this project transitioned from university researchers to district teacher leaders. These results illustrate that materials which contextualize learning and support student inquiry as part of an urban systemic reform effort can promote learning of important and meaningful science content aligned with standards. © 2004 Wiley Periodicals, Inc. J Res Sci Teach 41: 669–692, 2004