Writing is a key disciplinary practice in STEM used to construct scientific knowledge and communicate research findings. With its role in the scientific process, writing is often incorporated into STEM classrooms to train students in scientific writing. The importance of incorporating writing in STEM classrooms is heightened by the role it can play in supporting student learning of disciplinary knowledge and thinking. However, the characteristics of a writing assignment can shape how and what students are learning. Although faculty recognize the value of writing in instruction, they often face barriers that constrain the amount and types of writing they incorporate into their classes. This article describes the design and propagation of Writing-to-Learn assignments in introductory STEM courses at the University of Michigan through the MWrite program. Our aim is to present a framework that could inform similar efforts from the classroom to institutional levels. The Writing-to-Learn assignment design described herein incorporates a context-driven prompt followed by content-focused peer review and revision. We also describe the structures incorporated into the MWrite program to support the large-scale implementation of writing in high-enrollment introductory STEM courses.