I am a Parent and Child Advocate and Mentor, with two special needs children. Knowing your rights and the laws is pivotal. Next, knowing your child as well as you do. Think about what you want for your child. Make a list of their strengths and weaknesses (needs). Base the IEP on their strengths, and make sure that all of their needs are addressed in every category.
Don't focus so much on education. Think outside of the box. Think about your child as a whole person in every environment and situation. If they are good at something you would not ordinarily associate with school, it doesn't matter. That IS a strength. Include it. Weaknesses also. Include problem areas at home or in the community, not just in academics.
Never forget that once your child reaches the age of 14, you need to focus on the Transition Plan. Make it a good one, and make sure everyone on the IEP Team is headed in the same direction. Think about everything your child is going to need in order to live independently, function in society, and be employed. This is going to include employment training IN A FIELD OF INTEREST TO YOUR CHILD -- not simply what is available or only option offered. The IEP needs to include plans for living after graduation. This might include a group home or shared living arrangement, or an apartment -- so the team needs to help you prepare by getting your child on every support service waiting list, like for subsidized housing, or having an open case file with your county agency funding source.
Finances are critical. Your child will need an income. This could be from employment, or from SSI, so make that one of the long-term goals. Once your child turns 18 they will receive cash benefits.
If your child is going to need support, look into available waivers and get on the waiting list (Independence Waiver, Person and Family-Directed Waiver, Consolidated Waiver, Adult Autism Waiver).
Look into the legal aspects of adulthood. Will your child require you to have Legal Guardianship, or perhaps a Durable Power of Attorney?
Now is the time to prepare, and while your child is still in school, they (entitlement) are the responsible party.
Hopefully this will be some help for you.

Start pulling out info on your rights with IDEA. The IDEA website has information on rights for children with Autism. You should also look at the Office of Superintendent for Public Education and familiarize yourself with any additional "process" you can create for getting the attention at the district level. When you have your parents rights down for IDEA then study the process for going about the IEP. If he already has an IEP you can request a Re-Evaluation based on the new diagnosis. Do not give up and be persistent. Use clear and concise language for your district. Every state has their own way of addressing the process in terminology, but it should all be similar. We requested the Replication Process with our particular school district that moved us in the direction of Re-evaluation. Always take notes and follow-up. You may have to be in the man in the middle with communication between primary care providers and the district - be prepared to do that. Hope this helps. Let me know if you have an more specific questions.

Be your son/step-son's champion!

Establishing rapport with special ed teachers goes a long way toward getting good IEP goals, mods, and services. Every state is different regarding how IEPs are constructed and how decisions are made. I'd suggest connecting with your state's parent advocacy group (e.g. Parents Reaching Out, etc.) for a parent advocate to come with you to help you steer things in the direction of collaboration and effective programming.

Speaking from here in Alaska, if the School District tests you're child, which is the cheaper way to go, but then you're stuck inside their process until the end. I followed medical advice to have my Son independently tested as it provided better legal position beyond just an advocate if needed. Even with insurance it was expensive, but happy I took the advice.

After independently having our Son tested, the school district wasn't happy at all during our IEP meeting, and insisted to do their own testing. I let them go forth, and during our second meeting, their results were not different. School Districts have pre-designed "boxes", which is easier on the school budget but not right for our son specifically. They pushed for their model, but even the teachers disagreed with the school psychologist and special ed advice.

This is where the Independent testing benefit comes into play. I simply explained that I had my Son's independent tested and a plan of action which we and his teachers feel works best for him. It was disappointing to see opposition based on the fact this was outside their box, rather than look at the fact I'm engaged. All turned out well, but the power play was present for sure.

If I had allowed them to do the testing only, I wouldn't have had a leg to stand on or it would have been much more of a struggle. Specific support and resources require the school district to spend more money, and I get that, but we need to get the most we can at a reasonable compromise. Working together is most important, but felt better than to have cards in pocket where I felt it was necessary to play if needed.

RobMc, advocates were available through our independent testing office. I also had our Son's counselor as a resource as well.

IDEA uses the language "scientific" with regards to educating students with disabilities, so it is also important to go in knowing what is evidence based (scientific) in the educating of students with Autism. The National Autism Center has great resources including a parent's guide http://www.nationalautismcenter.org/

Also, a nice chart of the overall research base can be found here http://autismpdc.fpg.unc.edu/content/national-s...

Personally, I turned the NACs guidelines into a table and visited my sons' school self contained, inclusion, and an outside program for more serious needs and compared them side by side. I brought it to the IEP to fuel a discussion as to which settings were most appropriate for my sons needs.

In my opinion, public schools are not adequately trained and have too many types of needs in one place to be able to specialize for kids on the spectrum. I hope to create a charter school (school within a school) to address this need-particularly for the fastest growing category of high functioning autism.