Key competencies straddle an educational reform that has taken on a central role within the European Union. However, there is a lack of empirical instruments aimed at assessing preservice teachers' opinion of competency-based policies, their self-evaluation regarding such policies, and their understanding of the intended rationale behind competency mandates. Instruments with similar aims in other contexts suffer psychometric shortcomings. Therefore, the authors' aim was to design an instrument to examine primary preservice teachers' beliefs about the role of key competencies in education, self-evaluate their understanding of the concept of key competencies, and determine if they understood the intended interdisciplinary focus. A three-phase pilot (n = 295, n = 277, n = 263) was carried out with each phase aimed at progressively improving the instrument's psychometric soundness. Drawing from data obtained from the third pilot, the psychometric scale properties are reported for a much-needed assessment tool.