This presentation outlines the principles of optimal test design for creating a through-year assessment system. This system involves administering multiple tests at various time points during the school year. The goal is to establish a unified assessment system that delivers multiple tests with distinct objectives and specifications for instructional guidance and annual summative proficiency determination. The system illustrated is a hybrid interim-summative assessment involving multiple interim adaptive tests with different objectives and blueprint specifications. It provides both within-year instructional feedback and end-of-year summative proficiency assessments. Each test comprises multiple segments or phases, assembled adaptively using specific optimality criteria and distinct test specifications implemented as a mathematical optimization problem. The key design features address the need to use various optimization criteria, meet complex test specifications within and between tests, provide instructional feedback that aligns with test specifications, track individual examinees with customized test initialization, control item exposure for each examinee across test administrations, and transition item pools within and between test administrations when necessary. The system will be illustrated using an open-source R platform.