One positive step; you should make sure yiour son takes is to confirm with the company that they will give him a good professional reference, they are not allwed to give a bad one, but they need to know that from your son's perspective he had no reason to believe his training was not considered as up to their standard and he must also put in writing to them that he is expecting them to support his request for a psitive reference .
It is one thing he can leave the cmpany stewing over, as they have to have slid grounds for refusing to give a reference and cannot in law gice a bad one.
he can ask in writing for feedback from his training mentor and as the benefit agency will need to have his firm complete a reason for his dismissal officially they would need to be clear on the reasons and mit just verabally add them on,
industry is slowly recovering and I am sure he will find a position shortly, he is in a very empoyable position being young and newly trained as he is cheaper to employ and noit set in his ways, i would add that he would find a position in either the army airforce or navy within months if he was so inclined.