The emphasis on STEM in schools has led to conflicting pressures on science teachers to deliver high-stakes exam performance and to foster enthusiasm and career aspirations by making science relevant and meaningful to pupils. Some teachers run project-based activities spanning weeks or months, generally in addition to the standard curriculum and often in the ‘gaps’ or neglected spaces of the school timetable. I am using cultural-historical activity theory to understand how such activities develop, the various motives teachers and pupils bring to the activities, why difficulties arise and how (if) they are resolved. Agency is a key theme in my research.