For a school library to function as a support for the students’ development of their academic abilities, it must provide material satisfying their needs as well as the needs of the teachers. The school library should assist the students in their research endeavours, as well as inspire reading for pleasure. In order to do this it is imperative that the school library actively develops the existing collection and continually strives to meet the needs of its users. The aim of this Master’s thesis is to describe and reflect upon how a particular school library works with collection development. The study focuses on the material present in a specific library, i.e. the books and other media types used or sought there, and directly influences that library as the material is reviewed, organised and/or discarded. To collect data for the thesis an action research inspired strategy was used, mainly drawing inspiration from the four defining characteristics of action research as described by Martyn Denscombe: Practical (aimed at dealing with real-world issues), Change, Cyclical process (initial findings generate possibilities for change which, once implemented, form the basis for further investigation), and Participation (practitioners are involved in the research process). The study involves practical work at the school library in question, mapping the collection and reviewing user needs, which led to decisions regarding weeding and procurement. The updated collection was then evaluated through interviews with students and faculty. As a result of the study a policy for collection development was formulated to support further collection development in the studied school library.