Assessment of Transversal Skills in STEM (ATS STEM) is an innovative policy experimentation project, which aims to enhance digital assessment of students’ transversal skills in STEM. This Erasmus+ project is situated in primary and secondary schools across eight European countries, involving 12 partners on different levels of educational system. Teachers and researchers have collaboratively developed and piloted several integrated STEM learning activities all focusing on UN sustainable development goals. Embedding formative digital assessment of STEM learners’ work has been a central component. This paper provides an overview of the project and shares some results from Sweden and Ireland. We provide examples from practice that help illustrate the complexity with a particular focus on technology education.