ABSTRACT:  Traditionally, school libraries, in common with other libraries, have judged their effectiveness on flows, which are more a measure of workload than of library effectiveness. Libraries have to come to terms with the idea that converting knowledge to value might require that the amount and speed of the information that flows out of the library be reduced in order to provide users with quality “just for you” services. 21st century teacher-librarians need to be able to define and demonstrate value in the context of their libraries and demonstrate return on investment in terms of academic outcomes. A conceptual framework for value measurement is proposed, the deficiencies of current performance measurement practice are discussed, in particular, the tendency to gather information about process and to report in a way which obscures the value of the library to the parent organisation. A case study on designing, modifying and using a transaction based multi-faceted performance measurement mechanism is described. The rarity of linking personal performance evaluation to organisational performance is discussed and methods of doing so are proposed.