trying to work more on extension on hitting to the gaps.
If you give this one minute of thought you will realize that pushing your arms at the ball delays/prevents the bat head from getting ahead of the hands (ie. it slows the bat head). Pro players do not do this unless they mistimed a pitch, or misjudged an outside pitch.
"Son is in a slump. He is putting the bat on the ball "
If he is extending his arms, and hitting the ball, it's probably not being hit hard.
You want your biceps close to the torso during the swing.