Extended School Year (ESY) services are special education and related services that are provided to students with disabilities beyond the regular school year.
The purpose of ESY services is for students to maintain existing skills/knowledge and to prevent severe regression of the skills/knowledge acquired during the regular school year that, if lost, would significantly jeopardize the educational benefits accrued to the student during the regular school year. In order to receive ESY services, students must be determined to be eligible for ESY by their IEP team. Students with disabilities are determined eligible for ESY services through an analysis of body of evidence including retrospective data (data collected before and after school breaks which demonstrates severe regression after breaks from school and an unreasonably long time to regain or recoup their skills), predictive data (data based on Predictive Factors that suggest that the student is likely to experience severe regression over summer break without continued services) and circumstantial considerations.
More detailed information about ESY Qualification can be found in both slides and screencast versions.