If you think your child may need special education services, your first step is to request an evaluation. The special education or "IEP teacher" at your child's school can help you write the request--you can also ask the Parent Coordinator to help you. Visit the New York City Department of Education Website-Special Education
For student-specific issues, work with your child's teachers and principal, first. If you still have questions, dial 311 and ask for the Special Education Call Center.
Schools are required by Fed and State Law to advise parents of their right to mediation in addition or as an alternative to an impartial hearing for resolving disputes about their child's special education. The NY Peace Institute has developed a Manual to help you.