Agree with Yorkshirelass, there may be adjustments that could be made. Certainly there are in Universities - quiet rooms, computers rather than writing, extra time, etc.
I'd say the most important thing is to reassure him that whatever happens it is not the end of the world. Exams can be retaken.
I flunked my A-levels due to stress/depression/bullying/drugs. Would stare at books I had to revise and everything would go blank. Retook three years later off my own bat, at evening class. Passed them all, despite doing it in half the time with no revision. The stress had been removed, so it became a challenge rather than a chore.
