Blockchain technologies are increasingly embedded in everyday digital experiences, yet their underlying mechanisms remain opaque to young learners. We present Blockchain@School, an unplugged board-game-based toolkit designed to make concepts such as distributed consensus, immutability, and cryptographic security tangible via collaborative play. Developed through an iterative design process with educators, Blockchain@School combines physical blocks and cards with a lightweight web application for real-time validation. We evaluated the toolkit in a series of 90-minute workshops with more than 300 primary and middle school learners (ages 9–13), using pre/post questionnaires, structured observations, and teacher feedback. Findings indicate significant improvements in learners’ understanding of blockchain principles, alongside high engagement and effective collaboration. Teachers reported that the activities can be easily integrated into existing curricula and replicated in autonomy. Our work demonstrates how unplugged, game-based learning can lower entry barriers to emerging technologies, foster digital citizenship, and support scalable approaches to teaching complex computational ideas in K–12 education.