This sounds as if there has been some miscommunication. It appears your child is being considered for special education for the first time. If this is correct, then a committee, including yourself, would have identified areas requiring assessment prior to consideration of eligibility and then of placement into special education. This would include: educational testing, psychological testing, a social history of the child being considered (which could include birth history, school history, medical concerns, etc.), speech and language assessment, and even possibly an assessment for physical and/or occupational therapy.
 
If the school is asking for medical records, there is a reason for this. In order to qualify for special education, especially if qualification is being considered in the area of a learning disability, medical information may be critical. Sometimes schools consider another label called "Other Health Impaired." If this is the case, medical records are needed to support the documentation to allow a child to receive special education services, which will be fully expressed in an Individualized Educational Plan.  Give the school a call; talk to the psychologist, social worker, or school counselor. Ask them to help you understand why this typically private information is needed.