dropping of hands when hitting

Question
my 10 yr old son is getting very frustrated as we continue our all star tournament play this year.  he is known to be a good hitter but is in a big time slump.  we as a coaching staff have noticed that he is dropping his hands as the pitch is delivered and thus is upper cutting his swing and is a second too late on his swing.  despite reminding him over and over he continues to drop the hands as i think his body to so used to doing it that its second nature.  when he does actually make contact its usually a pop up.  what drills can he do to help correct this problem.  thanks for your time and effort.  not sure if this will help but hes a very powerful young boy with a big hard swing.

Answer
Putr him on a tee and set the ball about chest high.Have him take swings and if he hits the tee he is dropping his hands to low.This is a self teacher. Most people who drop thier hands dont or cant feel it happening.So you telling him will not mean anything.This will give him instant feedback.