19 Texas Administrative Code § 89.1065. Extended School Year Services (ESY Services). 

Extended school year (ESY) services are defined as individualized instructional programs beyond the regular school year for eligible students with disabilities. 

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(2)  The need for ESY services must be documented from formal and/or informal evaluations provided by the district or the parents. The documentation must demonstrate that in one or more critical areas addressed in the current individualized education program (IEP) goals and objectives, the student has exhibited, or reasonably may be expected to exhibit, severe or substantial regression that cannot be recouped within a reasonable period of time. Severe or substantial regression means that the student has been, or will be, unable to maintain one or more acquired critical skills in the absence of ESY services. 
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Last Amended:  January 1, 2015, 39 TexReg 10446  
Entered: Jan. 19, 2015