As I understand it, the appropriate steps to take in this case involve writing a letter to your son's school (the special education coordinator if he is in special education) asking that they meet with you to resolve the issue. Inform them that you have done your research, and you are not comfortable with your son being retained. The National Association of School Psychologists (see first link below) clearly states that the research does not support grade retention. Overall, students who are retained in comparison to students who are promoted despite academic concerns are more likely to experience problems in academic achievement, emotional adjustment, and behavior. Provide copies of the articles listed below with your letter.
You must be your son's advocate in this situation, and I wish you luck.
L. Compian, Ph.D.
Education.com Expert Panel