This ethnographic study reports on the findings from seven English secondary schools that participated in Project Faraday. The project was funded by the Department for Children, Schools and Families to build innovative learning environments to encourage students into upper secondary inquiry-based STEM. Despite the innovative classrooms, the schools emphasised A-Level university entrance science. Technicians prepared for specific science subjects, although teachers acknowledged the value of inquiry-based pedagogies. UK policies prioritising A-Level assessment were found to be impeding inquiry-based STEM, although wealthy schools had the resources to facilitating both A-Level science and inquiry-based STEM through clubs and co-curricular programs. Our data elicited important general design principles to inform makerspaces for inquiry-based STEM for adult learners. We concluded that initial teacher education programs should provide graduates with pedagogical experiences in makerspaces that enabled them to appraise contemporary school learning environments; and be informed about securing safe, flexible, and durable equipment for students.