It's hard for me to tell from your question if you want your son to be retained while he's being promoted to 1st grade or if you want your son to be promoted while he's being retained.
I think the most important thing is to talk to your child's teacher about why she decided to promote or retain your son. Your son's school likely has a "check list" of academic and social accomplishments a student has to achieve in order to be promoted. The teacher had to document which of those your son could and could not do. Even with that list, the teacher ultimately has to make a judgment call about whether or not the student will be successful in 1st grade. Ask for a meeting with the teacher and principal to find out why they made the decision they made.
Education.com has some great articles on grade retention. Hopefully one of them will help.