The question of how to scale up successful innovations remains a key challenge for policy and practice in education (Hall, 2013). This article outlines three established ‘schools of thought’ around how to scale up successful innovations. The first approach – eco-systems - is informed by complexity theory and tends to focus on generating and scaling innovations through diverse lateral networks which allow multiple stakeholders to collaborate (OECD, 2015). The second approach – ‘what works?’ – is interested in identifying effective practices through rigorous, scientific research and in replicating these proven practices across multiple schools with high degrees of fidelity. The third approach – Improvement Science - emphasises the importance of practitioner judgement and learning for interpreting and applying evidence across different contexts, but also recognises the importance of school-level cultures and wider factors, and so seeks to generate systematic forms of innovation, evaluation and improvement at scale (Bryk, 2015; Resnick, 2010). This article concludes by discussing the respective contributions of these models and the implications for policy, practice and research.