Hoovedawg--I asked my 13yo and he came up with his favorites. His team is hitting collectively over .500 so these have been very effective.
#1-one handed soft toss. Boys toss wiffles and batter works on one handed line drives. If he pops it, he chases the ball. They work on both hands.
#2-I have had my younger ones do soft toss with mini marshmallows.
#3--Cage game "Front side, Back side"
Off of live pitching. Front side each batter must have: 2 bunts, 1 fake bunt/slash, move the runner (hit behind runner) then score him (sac fly or hit). Get one point for each executed succesfully. Back side is 3 outs with the second out hitting a curve ball. Losers (usually bottom 3 guys have to complete some kind of task). Boys love this and are competing for top score.
#4 27 outs. Play a simulated game, pitcher throwing 1/2 speed. Coach hitting ball. Players are to run on off field, play each play like a game, keep each other up, etc...
Like I said, our guys are hitting the cover off the ball. It has been incredible to watch. Good luck.
