If you would like to have your child assessed, you must contact your local school administrator. The school administrator would be the principal or the special education program consultant. List your reasons for the request (what you suspect may not be typical) and request an evaluation. You must follow it up in writing. The request must be dated to document a timeline. The school district must have your request in writing to begin the process. When the document is received by the school district, the process must begin.
For more information regarding assessments and other disability rights, please refer to Community Alliance for Special Education (CASE) or Disability Rights California. This site addresses 52 questions regarding the assessment process. You might even want to bookmark this site or download the information.