Obligations of state education agencies (SEAs) and Part C lead agencies set forth by the Individuals with Disabilities Education Act (IDEA) pertaining to early childhood transition from Part C to Part B of IDEA are described in several regulatory and guidance documents including Part C draft regulations (34 CFR Part 303), Part B regulations (34 CFR Parts 300 and 301), and an Office of Special Education Programs (OSEP) policy guidance letter dated February 11, 2004. Requirements include providing data to document progress on Indicators related to early childhood transition as a part of a state's Annual Performance Report (APR) to OSEP. Indicator 8 on the Part C APR requires data to be reported on the percent of children exiting Part C who received timely transition planning that includes an Individualized Family Service Plan (IFSP) addressing transition steps, a transition conference and notification to the local education agency (LEA) if the child is potentially eligible for services under Part B. Part B APR Indicator 12 requires states to report the percentage of children who are referred by Part C prior to age three, found eligible for Part B and have an Individualized Education Program (IEP) in place by their third birthdays. These two APR indicators, C8 and B12, require states to have systems and procedures in place that allow them to collect accurate student-level data between two different programs that are often administered by different state agencies. Using unique identifiers that are assigned to children identified in Part C and remain assigned to the child as they transition to Part B is one aspect of data sharing that some states have instituted in order to improve early childhood transition outcomes for their students and the state's ability to report on indicators C8 and B12 specifically. This document reports on the experiences of six states that currently use unique identifiers within their data systems to track students from Part C to Part B and provides information on the circumstances surrounding the development of such systems, what the systems look like, benefits and challenges. (Contains 6 resources and 3 footnotes.)