This article presents the implementation of an assessment model for generic competences in K-12 enabled by open educational practices. It showcases a digital competence assessment model that outlines the design of competence assessment scenarios constructed by means of a collaborative process involving teachers from six European countries, learning designers, and researchers. Our study draws attention to the concept of open educational practices as a broad descriptor of four areas of teacher practice regarding design, content, teaching, and assessment. The process unfolds through three phases, where teachers' engagement with collaborative processes and network-based tools facilitate the construction of active shared learning. It analyzes the joint creation of open practices, and the production of open educational resources. The scalability, flexibility, and adaptability of competence assessment scenarios underline their transferability to similar contexts. The experience may benefit educational institutions and communities of teachers interested in innovating and opening up education.