Yes, I used an advocate and that was the only reason that we got an IEP. In fact, that's exactly, what the school said. They assumed I would start Due Process as the next step since I had an advocate, and they told me that did not want to deal with that. So, they gave me the IEP.
I tried on my own for two years to get an IEP and was not successful. The advocate had excellent, concrete ideas to implement for my child as well. Going in, I'd thought the school would know what my child needed. That was not the case.