This study, part of the 3-year Assessment of Science Competence project named NATKOM, employs a Design-Based Research (DBR) approach to tackle the challenge of assessing science competencies in Danish primary and lower secondary schools. Collaborating with 28 teachers from 18 schools and educators from University College Absalon, new formative assessment designs were developed and tested. Preliminary findings reveal teachers’ struggles in conceptualizing and assessing competence-oriented teaching. Six characteristics of competence-oriented science education are identified, focusing on concrete problems, clear competence focus, collaboration, freedom for students, reflection opportunities, and core science knowledge. Formative assessment emerges as the preferred approach, aiding in promoting effective learning and addressing challenges in observing student activities. Examples of formative assessment tools suitable for assessing science competencies is presented here. Challenges persist in implementing competence-oriented teaching, highlighting the need for continued support for teachers and assessment practices aligned with competence-oriented education.