When a school district refuses to honor a student with a legitimate Section 504 plan in place, it's time to contact a lawyer.
My fifth-grader has a Section 504 plan for ADHD. A neighboring school district provides "itinerant services" for students who have a Section 504 plan and I just found out my school district provides "itinerant services" only for students with an IEP. Why are there two very different interpretations of what services a district must provide?
This is one for the lawyers. I haven't heard of a school district successfully refusing to honor a student with a legitimate Section 504 plan in place.
You might want to look at attorney Lawrence M.Siegel's book, The Complete IEP Guide: How to Advocate for Your Special Ed Child. Siegel has a section in the back of his book that lists many legal resources as well as the exact wording of Section 504.
You can also learn more about the differences between the Individuals with Disabilities Education Act (IDEA) and Section 504 on FamilyEducation.com.