The theme of the conference Cross-Curricular Teaching: Curriculum Flexibility and innovation enables the discussion of Cross-curricular teaching is partially stated in national curricula. Even though the concept is mentioned, national curricula are still subject-based and the definition and orientations about cross-curricular teaching are unclear. The situation is evolving, several reforms/curricular reorganizations have been made, for instance in 2017 in the basic and secondary school in Portugal in order to institutionalise interdisciplinarity practices and curriculum flexibility. Therefore, cross-curricular activities are diverse in Europe, inside the same country, and even in the same school. It varies according to the level of teachers' motivation and involvement and their attitude towards the approach. It is often seen as something optional because of the lack of time. So cross-curricular teaching in practice can be interdisciplinary projects, co-planning, co-teaching, shared themes between subjects, extra-curricular activities. This scenario suggests many questions and comments about traditional subject-based teaching, school pedagogical autonomy and the professional beliefs of teachers. What would be the core motivation to implement cross-curricular teaching since the grading system is linked to subjects? Could a grading system based on competences be the answer?