The purpose of this resource is to unpack Part B State Performance Plan/Annual Performance Report (SPP/APR) Indicator 3D to better understand how to use it to improve outcomes for children with individualized education programs (IEPs). Indicator 3D is a new subcomponent of Indicator 3 in the Office of Special Education Programs' (OSEP) FFY 2020-2025 SPP/APR measurement table. This resource guides the reader through an overview of Indicator 3D, including how to calculate it and information on the setting/resetting of its baselines and targets. This resource also offers details about Indicator 3D such as where the data come from, how the APR Tool performs the Indicator 3D proficiency gap calculation, and considerations when analyzing, reporting, and using Indicator 3D data. As an aid to deepen learning, this resource includes examples with fictitious data. This resource will be useful to personnel in a state education agency (SEA) who are responsible for the collection, validation, reporting, analysis, or use of assessment data, including, but not limited to, the SEA director, SPP/APR coordinator, Part B data manager, EDFacts coordinator, and assessment program staff. This guide may also be helpful to those state staff charged with sharing information about Indicator 3D with internal and external stakeholders, including, but not limited to, colleagues at the SEA, parents and families of children with disabilities, members of the State Special Education Advisory Panel, local education agency (LEA) teachers and administrators, and external partners.