This paper proposes a theoretical framework for the development of curricula for Japanese heritage language schools. Although these schools provide most of the Japanese heritage language (JHL) instruction available to elementary and secondary school pupils, they have received little attention or support from the academic community. Specifically, they are in need research-based knowledge as well as models for teaching methodology, developing curricula and instructional materials, and providing teacher training. This paper examines recent theories and approaches in the fields of heritage language education, bilingualism, and instruction that is developmentally appropriate to young learners. The paper then proposes a process of curriculum design that integrates and applies these theories and approaches. The curriculum proposed here could also be used in heritage language schools for other languages. (Contains 2 figures.)