I am in the same situation as you and looking to put together a program for an 8th grader. A good place to start is reading the articles on Jon Doyle's web site
www.baseballtrainingsecrets.com.
I just started my research this week. I am going to put together a workout that can be done in an hour or less and incorporates all five of the phases below.
Would love to hear from other people who have already put together workout programs or have comments on what I have. Any help on combining the below into a couple of different workouts would be appreciated.
1. Dynamic Warm-Up: will include some combination of the below.
Walking High Knees
Walking Lunges
Walking High Knee Lunge
Walking Leg Kicks
Walking Side Lunge
Running Butt Kicks
Running High Knees
Running Carioca
Backpedal
Power Skip
Lying Scorpion
Arm Swings
Side Bends
Inchworms
Shin Grabs
Leg Overs
2. Active Conditioning: will include some combination of the below.
Jumping Jacks
Split Shuffles
Burpees
Mountain Climbers
Slalom Jumps
Pushups
Tire Throw
Tire Flip
Sledgehammer/Tire Work
Farmer's Walk
Sled Pull
Medicine Ball Throw
Wheelbarrow
3. Weight Training: will include some combination of the below.
Squat
Bench Press
Rows
Pulldowns
Overhead Press
Deadlift
Pullups/Chinups
Calf Raises
4. Core Work - Unbreakable Abs
5. Static Stretching