Inquiry activities generate rich opportunities for STEM learning and for assessment. When teachers pay attention to assessment information collected during the course of learning, they are able to interpret and make decisions about such assessment data in a timely fashion that can drive future planning and support student learning, for example through feedback. This chapter focuses on how classroom talk can generate evidence of learning and how teachers can utilise this to enable assessment to guide inquiry learning. It looks at several vignettes from different countries of on-the-fly interactions in inquiry settings and unpacks how teachers organised, facilitated and assessed learning in inquiry classrooms. Finally, the chapter considers opportunities, dilemmas and constraints that occurred as teachers attempted to integrate on-the-fly assessment into their existing assessment classroom practices. [For the complete volume, "Transforming Assessment: Through an Interplay between Practice, Research and Policy. Contributions from Science Education Research. Volume 4," see ED611936.]