Private supplementary tutoring became a widespread phenomenon in Japan during the 1960s. Since then, institutions providing tutoring known as "juku" have provided a wide range of services to supplement mainstream education. During decades of development, the shapes and functions of "juku" have changed in response to changes in schooling. Government attitudes towards "juku" have also shifted from rejection to collaboration, partly because "juku" have become so entrenched in Japanese society and can no longer be excluded from public decision-making processes. Collaboration between schools and" juku" is becoming increasingly evident in a series of neoliberal policy choices and socio-demographic changes. Patterns underline a government move to mobilize profit-driven "juku" to serve the public good. The inclusion of "juku" in public schooling necessitates reconceptualization of the roles of "juku" in the educational landscape. This article presents a conceptual framework based on an overview of the changing relationships between "juku" and schooling. It also identifies challenges in the collaboration, and explores implications for future relationships between mainstream and shadow education.