same question, retake SAT or not?

My son got 1550 on SAT.  The problem is that he got only 780 on math.  Should he re-take it in Oct to improve by 10-20 pts?  he registered for it, but does not want to take it.  he did not even want to take it last time.  but he will compete with those with 800 in math. i think he should do it.  our couselor does not think it is necessary.  

If he restakes it, can he just take math and skip reading/writing?  he was able to get 800 in math practice test last year. no idea how he did so poorly this time.   thanks