Technology companies are investing billions of dollars in educational technology, but also creating their own alternative schools. This article traces the emergence of four prototypical 'silicon startup schools' as exemplars of a technocratic mode of corporatized education reform: IBM's P-TECH, part of its Smarter Cities program; AltSchool, a chain of schools based on 'makerspaces' established by a former Google executive; Kahn Lab School, a new 'experimental' school launched by the founder of the online Kahn Academy; and XQ Super School Project, a 'crowdsourcing' project to redesign American high schools funded philanthropically by the wife of Steve Jobs of Apple. Startup schools are analysed as prototype educational institutions that originate in the culture, discourse and ideals of Silicon Valley venture capital and startup culture, and that are intended to relocate its practices to the whole social, technical, political and economic infrastructure of schooling. These new schools are being designed as scalable technical platforms; funded by commercial 'venture philanthropy' sources; and staffed and managed by executives and engineers from some of Silicon Valley's most successful startups and web companies. Together, they constitute a powerful shared 'algorithmic imaginary' that seeks to 'disrupt' public schooling through the technocratic expertise of Silicon Valley venture philanthropists.