A teacher-librarian (TL), school librarian, or school library media specialist (SLMS), is a certified teacher who also has training in librarianship. According to the American Association of School Librarians (AASL), a division of the American Library Association (ALA), the official title for a certified librarian who works in a school in the United States is school librarian.
The school librarian performs four main leadership roles: teacher, instructional partner, information specialist, and program administrator. In the teacher role, the school librarian develops and implements curricula relating to information literacy and inquiry. School librarians may read to children, assist them in selecting books, and assist with schoolwork. Some school librarians see classes on a "flexible schedule". A flexible schedule means that rather than having students come to the library for instruction at a fixed time every week, the classroom teacher schedules library time when the expertise of the school librarian, library and information skills, or materials are needed as part of a learning experience.
In the instructional partner role, school librarians collaborate with classroom teachers to create independent learners by fostering students' research, information literacy, technology, communication, and critical thinking skills.
As information specialists, school librarians develop a resource base for the school by using the curriculum and student interests to identify and obtain library materials, organize and maintain the library collection in order to promote independent reading and lifelong learning. Materials in the library collection can be located using an Online Public Access Catalog (OPAC)
This role also encompasses many activities relating to technology including the integration of resources in a variety of formats: periodical databases; Web sites; digital video segments; podcasts; blog and wiki content; digital images; virtual classrooms, etc. School librarians are often responsible for audio-visual equipment and are sometimes in charge of school computers and computer networks.
As program administrators, school librarians define, lead, and manage school library media programs by establishing library policies; overseeing the library budget; planning the physical and virtual library space; and maintaining a welcoming, positive, and innovative learning atmosphere.
In the United States, a teacher-librarian must have a baccalaureate degree and a certificate in secondary or elementary education, and must also complete a school library media program and gain a state certification. Programs in library science vary between institutions; however, state requirements must be met before a library media specialist is allowed to teach. Some school library media specialists hold the full Masters of Library Science (MLS) or Masters of Library Information Science (MLIS) degree, while others do not. In many instances, school librarians who have an MLS but do not have the requisite teaching credentials must obtain these teaching credentials and classroom teaching experience first before they are permitted to work as teacher-librarians, and often additional library science graduate coursework is required, focused specifically on issues pertaining to school librarianship.
Certification requirements vary widely from state to state, as does the title of the SLMS. Some of the coursework may include collaboration skills, cataloging, technology, collection development, children’s and young adult literature, advanced research methods, and various other topics.
The school library media specialist (SLMS) has the opportunity to become nationally board certified. The certification requires the development of a professional portfolio and, once certified, could increase the salary of the SLMS (Morris, 2004). This is a teaching certification, not a library certification. According to the National Board of Professional Teaching Standards, a person is only eligible to apply after they hold a Bachelors degree, have been teaching for three full years with a valid teaching certificate. (http://www.nbpts.org/become_a_candidate/eligibility_policies).
To alleviate the inconsistencies in state standards regarding media education and to encompass new teaching and learning challenges resulting from changes in information and technology, the American Association of School Librarians (AASL) created the Standards for the 21st Century Learner. This document, published in 2007, built upon AASL's 1998 Information Literacy Standards for Students to include specific skills, dispositions, self-assessments, and responsibilities for students.
Standard 1 relates to students' ability to think critically and gain knowledge through using a variety of technology tools to access multiple media.
In Standard 2, students use information to "draw conclusions, make informed decisions, apply knowledge to new situations, and create new knowledge."
Standard 3 states that students will "share knowledge and participate ethically and productively as members of our democratic society." Students use technology ethically to share information.
In Standard 4, students "pursue personal and aesthetic growth" by becoming inspired learners who seek information for personal enjoyment and growth. Students are encouraged to communicate their interests through a variety of means including the "social Web" or Web 2.0 tools.
Teacher-librarians rely on the support of local, state, national, and international professional organizations for career and professional development, employment opportunities, and awards/grants/funding. Groups like the International Association of School Librarianship ; the American Association of School Librarians, a division of the American Library Association; the School Library Association in the United Kingdom and the Australian School Library Association  host websites, publish journals, and sponsor conferences, workshops, and other events which showcase current research and practices in the field.
In the United States, teacher-librarians are also supported by state organizations which advocate for teachers at the district and school level. A comprehensive list is available from the ALA.