This study seeks to develop and validate an Assessment Centre (AC) tool for the evaluation and selection of school leaders, focusing on the identification of competencies that influence teaching and learning outcomes. International research supports the creation of Assessment Centres to select candidates for these roles, due to their superior predictive capacity over traditional methods. In this research, a model composed of four face-to-face instruments (an interview to assess competencies, a human resources exercise, a class observation exercise, and a strategic analysis exercise) was designed and validated which simulated the key tasks of a school principal. To establish the desired performance outcomes, three competencies and 15 indicators were selected, based on international and local standards. The analysis of performance results was obtained from a sample of 164 participants made up of teachers, school leaders and principals. The results suggest positive evidence for construct validity, concurrent criteria validity, and reliability between evaluators. Moreover, the data obtained from a sub-sample of principals, with three or more years of experience in their role, allowed for the association of their AC scores with the results of their school organisations, as measured by the National System for the Measurement of Educational Quality in the years 2013 and 2016.