Teaching players to hit curve balls

First you need to figure out why they aren't hitting it - are they not seeing it out of the hand, are they not staying back or are their mechanics changing?

Not seeing it out of the hand I would have batter stand in on bullpens (with a helmet) and have them load then call out pitch type and if ball or strike.  This helps with the seeing and recognizing part.  More reps leads to better recognition

Not staying back I would do drills to teach the separation of the load versus the swing.  It could be something as simple as tee work.  Set the ball up to break away from RH hitter on the outer half then say load and pause for a second or two then hit the ball to opposite field.  

Mechanics changing would be a lot of the tee work, soft toss, front side toss and anything that will teach a repetitive swing regardless of pitch type.

Others will follow with tons more / better advice.  I don't have much time to put more than this.  Stupid job

The JUGS is repetitive so the players will eventually learn how to hit a ball that they know is coming.  I prefer the Sports Tutor HomePlate pitching machine.  You are able to program several pitches and use the random feature.  The hitter does not know the next pitch and will force him to recognize the spin of the ball.

I don't know if this would work in high school or be well received. I taught my son to hit curves when he was ten. Based on his dominance I knew he would be seeing curves the following year. 

I bought a bag of whiffle balls. I pitched him BP in the driveway. The break on a whiffle ball is very exaggerated. I constantly reminded him to keep his shoulder in and drive the ball up the middle.

When he got older I taught him to guess curve at times and rip at it for a long drive. If a hitter guesses right or catches a hanger he can give it a ride. A curve sometimes sits out there screaming "drive me!"

A lot of the players that have played for me are proficient at hitting curve balls.  I believe there are many ways that this has come to develop.  Batting stance, I like a wider batting stance to comfort zone.  Stride, I see a lot of players with different strides that work, but the main thing I look for is how much does the height of their head dip during stride.  If their "camera" or eyes and head are moving too much I have found that these kids struggle with curve balls.  I do not use a Juggs machine but I cant throw a slip change from 40 feet that mimicks the path of a curve ball without stress to the old man's arm.  In BP i will throw about 10 curves in a row then I start the sequence 1,2,1,2,1,2,1,2,1,2 so that the player can see the difference in rotation of the ball and release of the ball.  The player has to recognize the difference.  One of my favorite drills that I think helps is the Tony Gwynn Drill (soft toss from behind the plate).  This makes the players stay back and attack.  We want the player to wait, wait and attack when the ball is at the front of the plate.  If they get long, transfer early or have slower bat speed, the batter will struggle w this.A new drill that I just started is angle toss.  Player stands with feet parallel to third base line then tries to hit ball rigt back at L screen.  The Mets hitting coach start BP with this every day.  Finally, they have to understand about getting hit with the baseball.  practice 1/4 turns with tennis balls and wiffle balls.  Important is that the player has to understand that if you want to hit a curve ball you will have be willing willing to be hit by a baseball, period.  What if  a kid cant hit a curveball?  No problem, but  he BETTER be able to hit 1 mistake, and do not take strike 1, unless it is a curve ball.  I do not see many pitchers that throw 3 curve balls for strikes.  So, hit the fast ball son, and never say "that was a nice pitch, and nod your head," that is losing the baseball battle.  Swing at fastball strikes, come out of your shoes on strike 1 and 2, go middle away w a wide stance after strike 2.  

Ty all for your input...would love to have the pitching machine mentioned above...but as we are a VERY small school i have limited resources....as for me throwing curves my days are over ...blew my shoulder out years ago...and i'm a lefty ...in our league their are currently no left handed pitchers that we will face.......  

SWV gave you some great drills that don't require a machine.  My son's hitting coach played professional ball for over 10 years and made it to the bigs for a short stint.  He is by FAR the best hitting instructor I have ever been around.  He used these exact same drills.  They worked great and my son became very proficient on off speed pitches.  The coaches favorite saying was, " Let it break then hit it just like a fast ball."  In order to do that, the batter has to learn to stay back and then attack the pitch.