First thing, A lefty with a slider is a good thing, more effective against left handed batters than a 12-6 curve...and with the proper location the back door slider or one that shoot beyond the inside corner to the right hand batters...location location location...with his above avg. fastball, a good change up, will be his ticket to the next level..Now I'll answer your question....Sounds like it's more of a wrist postion than arm postion...Since he already can throw a slider, he understands spin..the slider comes out of the hand just like a fastball, in order to get the 12-6 spin you **** your wrist inward...rest your elbow on a table with your arm pointing upward with your wrist go limp, this is the position your wrist and arm must be in at deliverly...get a baseball, tape or draw a circle around the ball, begin short throws and extend the distance when he can make the circle around the ball apprear to have a straight line as the ball is in flight. and even had him try to over exagerrate getting on top of the ball. Like I said, sometimes it works, most of the times it doesn't. He has really small hands and I'm wondering if this could be part of the problem? Does anyone have any tips or has anyone dealt with someone like this? Thanks in Advance.