The last ten years in school library research reflect an expanded definition of information literacy along with a stronger emphasis on in-depth information literacy development, concluding that a fundamental shift in instruction provided by school librarians is needed; one that not only helps students find information, but develops students' abilities to interact with, and learn from information, engaging with it in critical ways. Collaboratively designed and implemented through an instructional partnership between the school librarian and a classroom teacher, Guided Inquiry instruction helps students gain meaningful understanding and develop a personal perspective by exploring, comparing, and contrasting multiple information sources. Despite the frequently touted benefits of instructional partnerships between school librarians and classroom teachers, these structures are rarely, if ever, modeled by school library and pre-service teacher educators. This study examined the process and challenges inherit in designing and modeling Guided Inquiry units of instruction, through a school librarian instructional partnership model, in pre-service teacher education, exploring its impact on teacher candidate willingness to identify school librarians as co-teachers. Findings from the present study indicate Guided Inquiry units co-taught by school library educators and teacher educators help teacher candidates both successfully navigate the research process and develop a mental model of the school librarian as a co-teacher.