This chapter provides an overview of psychometric test construction, situating the Coaching Effectiveness Scale (CES) within measurement science. It explains how latent constructs such as attitudes, abilities, and personality are systematically translated into measurable variables. The staged process—construct definition, item generation, validation, standardisation, and refinement—is described, highlighting its iterative nature. Classical Test Theory (CTT) is introduced, with discussion of reliability, validity, and practical challenges in applied contexts. The chapter integrates conceptual, methodological, and statistical perspectives to show how rigorous test construction ensures scientific quality while meeting organisational needs. The CES is presented as a practical example of applying psychometric principles to create evidence-based tools for assessing coaching effectiveness.