To teach science writing effectively, scholars encourage combining writing to learn with applications of the science writing heuristic. How teachers learn to do so remains under-examined. This essay follows a cohort of ninth-grade science teachers who collaborated in a project to develop, test, and revise such a combination of writing prompts for physical science and biology in a high-poverty, urban school district. Students in the project acquired course concepts more readily. In standardized exams designed by the district, they also outperformed students enrolled in the same courses, using the same district curricula. Even special education students demonstrated better progress and retention. In addition, the exams enabled the science teachers to evaluate the curriculum and to consider how writing to learn could redress its weaknesses. Preliminary results of the project suggest that writing to learn--augmented by locally designed standardized tests--might not only transform student learning outcomes, but transform the development of secondary science curricula as well.