Curricula are one of the most widely used educational inputs, yet few are developed and evaluated scientifically with a dearth of programs targeting academic language. This manuscript describes an iterative approach to the development of a tiered academic language curriculum supplement for prekindergarten (pre-K) and kindergarten (K) students. A series of four studies were conducted to iteratively design the curriculum following a framework for developing research-based curriculum; however, we modified the framework to focus on efficiently preparing a curriculum for large-scale use by teachers with diverse competency levels. Findings from the first three iterative design studies include the benefit of overdevelopment to retain only the strongest content and the need to consider both beginner and more advanced teachers as end users. Results of the final pilot (N = 1,193 students) show strong effects on taught vocabulary words (pre-K: d = 1.29; K: d = 0.84). Teachers had positive responses to the curriculum, but they did not generalize use of research-based practices during a transfer task (shared book reading lesson). Implications for developing curriculum are discussed.