The goal of this study was to understand how school librarians and classroom teachers co-teach to facilitate learner-centered instruction, including inquiry and maker learning. Research was conducted through interviews and field observations over three years. In this study, the participating school librarians and teachers worked together throughout the instructional processes--from planning to implementing to assessing. A significant piece of the co-teaching occurred through co-planning, both prior to and throughout the units. During implementation of the units, the school librarians led instruction, provided individual coaching, and assisted with classroom management. The educators collaborated on both formative and summative assessments, before, during, and at the end of the units. The school librarians used various instructional methods grounded in cognitive apprenticeship, such as scaffolding, modeling, mentoring, and coaching. The educators brought differing expertise to the co-teaching relationships. The classroom teachers were the content-area experts, and the librarians' expertise included the processes, approaches, and technologies for the inquiry and maker learning. In these areas, the librarians mentored and scaffolded the classroom teachers. These co-teaching relationships evolved over time, as the teachers gained experience in inquiry and maker learning. The findings suggest librarian-teacher co-teaching significantly facilitates learner-centered instruction in schools.