1. Look at Attorney Lawrence M. Siegel's book, The Complete IEP Guide: How to Advocate for Your Special Ed Child. He has many suggestions for cutting through stumbling blocks like this.
You can also contact one of the learning disabilities parent advocacy groups and ask for their assistance. They may be able to refer you to an independent tester who has had success in giving students a more comprehensive evaluation that can pick up the weaknesses getting in your son's way in school. They may also refer you to an advocate who can walk you through the process of contesting the decision of the school district. These advocacy groups may also be able to direct you to free or low-cost tutoring services. Often these are provided by people in training (under supervision) and may be located at colleges, universities, or community service organizations. Call the Coordinated Campaign for Learning Disabilities at 1-888-GR8-MIND for more information about organizations in your community. You can also check out the Learning Disabilities Association of America at 1-888-300-6710 or the International Dyslexia Association at 1-800-ABCD123.
FamilyEducation.com provides information about learning disabilities and special education that would be helpful to you. While you're at it, your son might want to have a look at www.ldteens.org where he will have an opportunity to share with other students his age who are having similar difficulties.
2. You can ask your school guidance counselor about accommodations that could be granted under Section 504 of the Rehabilitation Act of 1973. These accommodations (e.g., using extended time on tests so he can use strategies like underlining key points or using pre-writing strategies to organize his thoughts before he writes) could be granted under this law. He would still have to be identified as having a disability under this act to get these accommodations, but he would not be granted special education services like speech. Sometimes, however, if special education providers do not have full caseloads, they will take students "at risk" and provide them with services.