The WiS Co-Planning Tool is a research-based tool to help special educators and their science educator colleagues plan writing instruction in a way that offers solutions to barriers of including writing instruction in science class. The Tool is aligned to the nature of science, the NGSS and CCSS for writing, and inclusive of struggling writers and students with disabilities. Using the tool, co-teaching teams can actualize the components of effective writing instruction in science to: (a) prioritize writing as an integral part of science instruction, (b) assign writing tasks most likely to promote deep learning to optimize time spent on writing, (c) teach writing by implementing evidence-based practices, and (d) adapt writing instruction to provide additional supports for students with disabilities. The Tool was developed based on a synthesis of research-based practices for writing in science and the results of a national survey of science teachers. Step by step instructions are provided throughout the manuscript.