You should consult an attorney immediately. If you cannot afford one, try to talk to his public defender. The DA is not required to give him an offer, but the attorney should try to talk to the judge to see if a deal can be reached.
I agree with both attorneys. If you and your son are not happy with the representation, the Judge will usually give you time to seek out your own lawyer. Many times however the DA will make an offer on the day of trial.
Something is missing. The DA ALWAYS offers some sort of a deal. It may be a good one or it may not be, depending on the evidence, but there are always offers discussed.
I don't know what the evidence is against him, but if the case is strong, he (and his attorney) may want to take a deal. If there are weaknesses in the case or the DA can't prove it, then it may be headed to trial.
The above answer is for general information only and is based on the information you posted. Every case is fact dependent, so to get a thorough analysis of your situation, you will need to consult face to face with an attorney licensed to practice in the jurisdiction where the incident took place. Do not conclusively rely on any information posted online when deciding what to do about your case.
My colleagues are correct- if your son is unhappy with his representation he should consider hiring a lawyer. Are you sure there was no plea offered or did he reject a prior offer? I agree that something is missing here.