In Europe, with the dissemination of curriculum autonomy policies, teachers tend to be more involved in curriculum reforms as curriculum designers. In Portugal, in 2016, the government unprecedently commissioned eighteen teachers' associations to define a curriculum benchmark -- 'Essential Learning'. Studies have shown the difficulties felt by teachers in their role as curriculum designers due to a lack of the knowledge and skills required to enact collaborative curriculum design. However, few studies have investigated the kind of knowledge, skills and support teachers need for curriculum design. This paper aims to present a theoretical model of the knowledge and skills required for curriculum design at the macro-level, verify to what extent the eighteen associations master them, and describe the type of support that teachers need to design the curriculum. For data collection, the focus group technique was applied to the teachers' associations and to two curriculum experts hired by the Ministry of Education to support them. The results show that the associations had difficulties in three domains of knowledge and skills, regarding curriculum design expertise, pedagogical content knowledge, and knowledge required to create external curriculum consistency, presenting some guidelines to increase the quality of curriculum design in future curriculum changes.