This paper provides both a summary and plenary paper for a Special Issue of papers that build on the findings of a research project that investigated formative and summative assessment methods to support and to improve inquiry-based science teaching and learning. The paper aims to unravel some of the complexity that underpins classroom assessment practices as teachers bring change to their pedagogical approaches, taking into consideration both the variability and variation in interpretation of both processes by STEM teachers across eight countries. By engaging with research processes, in collaborative working groups in each country, teachers were better equipped to face the practical challenges they encountered in their various contexts, strengthening both their processes of critical reasoning and exercise of professional judgement. We draw from this interweaving of connected professional ideas and nested practices, a consideration of those factors which seem most pertinent in terms of formality, temporality, response and desired outcomes. As such, the paper provides a directive that highlights how the development of inquiry competences and the skills to negotiate productive pathways through an inquiry activity can be informed, developed and enhanced by formative assessment. Such developments require pedagogic moves that allow student agency while fostering advancement through guided feedback.