How do I get my son changed from a 504 to an IEP?
An IEP is based on your son meeting the requirements of your school system to be identified as having a specific disability.
Under the school law, IDEA, services and accommodations must be provided once a disability is identified. This IEP spells out what services and accommodations will be provided.
Section 504 is based on another law, now called the Americans with Disabilities Act. Under this law, if someone has a disability, he or she must be provided accommodations (services are not mentioned).
So, go back to your school professionals and clarify for yourself why they do not believe that he meets the criteria to be identified as having a disability. Without meeting these criteria, an IEP will not be considered.