This book responds to the expansion of dual language immersion (DLI) programs into secondary contexts, examining the effectiveness of these programs and highlighting areas for improvement in the curriculum. Focusing on Mandarin Chinese DLI in Utah secondary schools, it presents the views of teachers, parents and students on the newly implemented program, explores patterns of classroom interactions, and assesses learners' oral narrative development as well as their learning strategy use in building reading, writing and listening skills. In this way, it pinpoints possible weaknesses in the curriculum and current teaching practices and provides pedagogical implications and suggestions for in-service teachers and administrators, advocating for the inclusion of heritage language maintenance as a program goal. It enhances pre-service teachers' understanding of the policy background and current program issues and offers a base for DLI researchers to build upon in understudied secondary school contexts.