I do train a lot of teenage athletes. The first thing to do is to improve their lifting technique and to build a base of muscle mass. Teenagers without a proper foundation of training cannot use the same programs as more advanced athletes.
The problem is that teens all like to show off, be the stronger man. So they often train the wrong way.
I use the following methods during the first 8 weeks of training to increase their muscle mass and force them to learn proper lifting technique:
Weeks 1-2: Paused reps - perform basic lifts (squat, bench, rom deadlift, barbell rowing) and hold a 5 seconds pause during the eccentric portion of the lift, around mid-point of the ROM. The pause will enable to athlete to feel the position and will make is easier for the coach to assess the lifter’s technique. The pause will also make subsequent technical corrections by the coach easier to “feel” by the athlete. Since this method is difficult, it’s impossible to use very heavy loads. So the athlete learns to lift correctly and not with his ego.
Weeks 3-4: Slow eccentric reps - once again perform the same basic exercise, performing the eccentric portion in 5-8 seconds and the concentric portion in 2 seconds. The relatively slow lifting pace will once again make the athlete aware of his body position and thus of his lifting technique. This techniques allows for slightly heavier weights than the preceding technique: so the athlete will be more motivated to train. However it’s still a difficult technique which will no allow the use of very heavy weights yet.
Weeks 5-6: Contrast reps - Sets of 8 reps. Reps 1-2: 604 tempo, Reps 3-4: explosive, Reps 5-6: 604 tempo, Reps 7-8: explosive. We are once again limiting the weight the athlete can use, and working on his technique with the slow reps. But we are gradually including the idea of explosive lifting into the program.
Weeks 7-8: Regular lifting in the 6-8 reps range.