The 2021 revision of the national computing curriculum in Czechia reaffirmed the importance of teaching fundamental computing principles, including principles of computer hardware, at the ISCED level 2 (ages \(\sim \) 11–15). Although these topics were present in the previous Czech curriculum, schools continue to face a shortage of structured, constructivist and evidence-based teaching materials that actively engage students in meaningful learning. To address this need, we developed three model lessons designed to help students grasp principles of core hardware concepts by building on their existing preconceptions. These lessons follow the constructivist Evocation – Realisation of Meaning – Reflection (ERR) framework, encouraging active exploration and reflection. The lessons were implemented and refined through design-based research in six schools across seven classes, involving approximately 160 students. Pre-post testing revealed large immediate improvements following the intervention ( \(n=45\) , Cohen’s \(d = 0.79\) ). This paper presents model lessons and impact of these lessons, contributing to the advancement of constructivist approaches in computing education at the lower secondary level.