Perhaps you've heard the terms 504 and IEP used to refer to your child's special education.  What are these terms? Wrightslaw has a complete listing of the difference in this link, but here's a quick summary:

The 504 plan simply provide access to a "regular education" for your disabled child. The 504 plan gives much weaker legal protection to the disabled child. A child's 504 education plan can be changed without consulting the parents. The disabled child is also much more easily expelled or suspended in a 504 plan.

An IEP, or individualized education plan, has all the benefits of a 504 plan. However, the child is now also protected by federal IDEA law. The IEP provides "educational benefits" based on the child's unique needs, not just access to a regular education. The school or institution must notify parents of legal changes. The family can also use IDEA legal safeguards if there's a dispute with the school.

The IEP is a legal contract of what the school district is to provide to the disabled child. Each and every part of the IEP should be done by the school.

The 504 or IEP makes no difference in your child's ability to be in regular or special education classes.

 In general, then, 504 plans apply to children who have mild disabilities. If you have been asked to switch to a 504 plan but have any doubts about the change, please contact a local autism support group or advocate for help.