China's rising economy has increased the popularity of learning the Chinese language. Chinese immersion programs have gained popularity in K-12 education, particularly for younger learners. However, research on the optimal instruction design for Chinese and English biliteracy development in one-way Chinese immersion programs is scarce. This Educational Leadership Portfolio (ELP) adopted the method of a case study. Two sample programs were recruited to explore the ratio of the two-program language used in the instruction design in order to understand how two-language allocation decisions affect Chinese biliteracy development. The study collected students' data on the state accountability assessment of English Language Arts (ELA) and summative assessment data of Chinese Language Arts (CLA) for three consecutive years from 2017 to 2019. Both programs' immersion teachers participated in an online survey to obtain contextual information on (a) the ratio of the two program languages used in daily instruction, (b) the instruction time schedule for CLA and ELA, respectively, (c) professional development (PD) on literacy instruction, and (d) literacy instruction strategies. By drawing on the teacher survey results and students' assessment data of the two programs, the study suggests that instruction design played a crucial role in Chinese literacy development. The effects of instruction design are reflected in early literacy development, adequate instruction time for CLA, and two languages transfer in teaching academic subjects. In light of the study's findings, recommendations are provided for crafting an instructional design that integrates early oral language development, protected CLA instruction time, as well as academic subjects taught in both languages. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]