I would make him understand that this was one opportunity but in future there are many more opportunities so not to get upset and should concentrate on future studies for better grades . He should not blame anyone for his less grades as he is himself responsible for not studying well for exams. It is a lesson for him ,and should take it as positively and study well next time to perform well . I would sit with him to study and make him understand , if he is facing any problem regarded to the subject. And tell him that he should pay attention in the classes of teacher and should blame any one for any mistake which is in real done by us .
hope it help u.