ACT vs SAT

My son did fine on ACT. Should I ask him to retake SAT? He has a SAT score from 9th grade, decent but not great.

He will apply for very selective colleges.

If his ACT score is competitive for those colleges he will apply to, there’s no need to take any more tests. If it could improve, it makes more sense to study and retake the ACT. There’s no need for him to bother with the SAT anymore, especially if he’s better at the ACT.

What are his scores?