Calves are the hardest muscle group to transform. Historically, humans had to walk for hours each day. The ankle joint is primarily solicited during that action. If all the effort of propelling your body was provided by a muscular effort of the calves, they'd tire out too fast.

That's why the Achilles tendon is so stiff and strong: it's the stretch-reflex of the Achilles that does a large part of the work at the ankle joint. The same thing that makes locomotion efficient also makes it hard to make the calves grow. The Achilles has a very strong and highly reactive stretch-reflex. When you do regular reps on calf exercises, it's that reflex that does most of the work. As a result, the muscles themselves don't contribute that much, thus they aren't stimulated optimally.

Furthermore, the range of motion on calf exercises is very short. If you do 8-12 reps, the time in which the muscles are under tension is too short to stimulate maximal hypertrophy. Lastly, the fascia surrounding the calves is the tightest of all the body. If it's too tight it can actually limit muscle growth.

The Solution for Puny Calves

1. Take the stretch-reflex out of the equation. A 2-3 second pause in the stretched position can greatly inhibit the stretch-reflex. The stretch reflex is activated to protect you from tearing yourself apart. A sudden stretch is what activates it. If you pause in the stretched position, your body sees the situation as safe and under control and the reflex will be inhibited. By pausing at the bottom of each rep you shift the work mostly to the muscles.
2. Initiate the concentric (going up) portion of the movement slowly. You just de-activated the stretch-reflex by pausing, don't reactivate it by jerking the weight up in a stretched position! The first inch of movement should be slow.
3. Extend the time under tension. Do 10-12 reps for calves, but hold the peak contraction for 2 seconds on each rep, actively squeezing the muscle as hard as you can. That will extend the TUT up to around 30 seconds per set. On your last rep, hold that peak contraction for 10-20 seconds. That takes care of the time under tension issue.
4. Relieve fascia tightness. Do loaded stretching when the muscle is pumped. After your set is done, get out of the calf machine for 3-5 seconds, just to let blood and fluids inside the muscle, then go back on the machine and hold the low/stretched position for 30-45 seconds.

Do each set like this:

1. Perform 10-12 reps with a 2 second stretch at the bottom and a 2 second peak contraction at the top.
2. On your last rep, hold the peak contraction for 10-20 seconds.
3. Get out of the machine, wait 5 seconds, and get back on it. Hold the stretch position for 30-45 seconds. Three sets total is all you need.