1EdTech has its roots in the IMS OneRoster specification. OneRoster has very broad adoption in K-12. The IMS certification of OneRoster compliant products is essential in establishing real interoperability. However, experience has identified some weaknesses in that certification and that there are many proprietary extensions being used. 1EdTech is designed to remove these weaknesses and to ensure guaranteed interoperability as part of the system procurement and deployment process. A key feature of 1EdTech is characterization. Characterization builds upon certification but provides a detailed, precise, definition of the interoperability capabilities of a OneRoster compliant solution. Furthermore, 1EdTech provides a way for users to use these Characterizations to compare and visualise the compatibilities, and more significantly, the incompatibilities between the systems that are required to interoperate. Ian Weddell, the 1EdTech Program Manager, and Phil Nicholls, the 1EdTech Architect, will explain how 1EdTech achieves this characterisation for OneRoster. They will demonstrate how vendors and K-12 Districts will use 1EdTech to achieve guaranteed OneRoster interoperability. Attendees will learn how 1EdTech can help then deploy better rostering solutions in K-12.