Full custody ?

You should be asking an attorney, not Yahoo Answers

If the father's name isn't on the birth certificate you probably already have full custody. If he's never challenged you in court for custody you're surely considered the sole custodian. The school just needs to see his birth certificate so they know you're the parent.

you hire a family law attorney. And if paternity hasn't been proven by a DNA test, then the Courts won't recognize him as your child until that DNA test is completed. You have to pay for it and you have to go through the lab that the Court specifies.

i would ask the school how they want you to do it

I would think the birth certificate would be enough.

you will probably have to check with a county clerk

Go back to court

Well, talk to a lawyer, but I don't see why you NEED such papers. If the father is not in the picture, what's the issue?  Even if he is, why would the school be demanding such papers if the father isn't even on the birth certificate and doesn't carry his surname? 

So, what's the explanation from the school?  In any case, take the problem to a lawyer.