I agree with Sweetie, if you can't find just the right article to back you up, bring what you can, then go and talk to the principal. Offer to sign an agreement that says you understand that you are putting your child in a class the school feels he isn't ready for and that you understand that he must prove he is placed appropriately in order to be allowed to stay in the class past date X. Often times the school is more willing to accept these "stretches" if they know you are not going to blame them if it doesn't work out and your child doesn't get the grade you think he should have. (Yes, they really want you to give them reassurances that they will have an excuse to shift blame if something goes wrong.) I would also try and talk to the science teacher. You may be surprised at how helpful they can be. It would be helpful to your cause if your son came with you to show that this option is something he wants and it is not just a parental request.
