http://www.wrightslaw.com/topics.htm --What's IDEA? What's a 504 plan? What are my legal rights? This is a big website with links to special ed law and related topics.
https://www.disabilityrightstx.org/ --Check out the IDEA manual and other "helpful resources" listed. Also, if you live in the Austin area, meet financial criteria, and have a case they can handle, they might help you for free. They also have free ARD meeting training on occasion with free childcare. Disability Rights Texas is the federally designated legal protection and advocacy agency (P&A) for people with disabilities in Texas.