Adopting and adapting: school leaders in the age of data-informed decision making Cornelius Young 1 & Gerry McNamara 1 & Martin Brown 1 & Joe O’Hara 1 Received: 9 April 2017 /Accepted: 24 April 2018 /Published online: 26 May 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract The concept of data-informed decision making (DIDM), a term used inter- changeably with data-driven decision making (DDDM) and data-based decision mak- ing (DBDM), is relatively new to Irish education and the school planning process. This research sought to clarify what data principals use and how they use that information for school improvement considering new school self-evaluation requirements. The paper begins by charting the rise internationally of data use in school planning, decision making and accountability. It proceeds to describe the policy context in this area in Ireland and then reports recent research with school leaders around how data is collected and used in their work. Although the paper focusses on Ireland, it is tentatively suggested that school leaders, teachers and policymakers in other countries, and there are many, which have come late to the expectation that school improvement and accountability should be heavily data-informed may find the efforts of Irish principals in this regard of interest. Keywords Assessment . Evaluation . Data-informed decision making . Leadership . School inspection . School self-evaluation 1 Introduction The concept of data-informed decision making (DIDM), a term used interchangeably with data-driven decision making (DDDM) and data-based decision making (DBDM), is relatively new to Irish education and the school planning process. Obviously, making decisions has always been an integral part of leadership and school development, but, Educ Asse Eval Acc (2018) 30:133–158 https://doi.org/10.1007/s11092-018-9278-4 * Cornelius Young cornelius.young7@mail.dcu.ie 1 EQI – The centre for Evaluation, Quality and Inspection and DCU Institute of Education, Room F217, DCU St. Patrick’ s Campus, Drumcondra, Dublin 9, Ireland