Trampoline and dry land equipment makes possible much faster repeats on dozens of skills. It also enables the spotter to make verbal correction comments about what the diver is doing. If we add to this the support of a TIVO set-up, this dimension lets the diver also see what it is the spotter is talking about. "A picture is worth a thousand words."
There are also various refinements that can be made to the formula above. Taken in systematic order and according to the nature of the equipment, we can start on trampoline.
1) trampoline: Basic skills, such as learning to bounce in rhythm with the tramp bed, executing elementary "tricks", such as forward or back jumps, with the upper torso erect, toes pointed, arms sweeping through the press while the eyes remain focused on the appropriate target. These skills can be quickly added to, according to the adaptability of the diver.
Basic maneuvres, such as front and back landings, with body aligned correctly, eyes focused on appropriate targets, can be learned in minutes, as opposed to the time it takes to come up from the bottom of the pool, climb out, get on the board, ready oneself for the next attempt. The recovery time needed to get ready for the next attempt is reduced by ½ to ¼. Magnified to a comparison between time spent in a springboard diving environment and time spent on trampoline or dry land board, one can complete three to five times the number of attempts on tramp or dry land board that one can complete from a board into the water. A fifteen minute workout in the tramp and dry land environment can be worth the same work out off a board that takes as much as one to two hours.
Front and back landings, combined with work on indispensable dives, such as back dive pike or tuck, can be done first with a hand spotter, then either with a belt and rig, or alone (just on tramp). The come out can be learned without having to go through the possible agony of that first attempt off a board. You work on your come out technique, until you can kick and shove at the right moment, then hold your head in for the landing. That means you have only one or two things think about for the entry, instead of four or five things. Make as many things virtually automatic, so that you don't have to sweat so many details in the same nanoseconds it takes to hit the water.
Self awareness: The diver can judge for him or herself by merely taking into account whether the maneuvres attempted seem successful. This can be considerably enhanced by the feedback from the spotter or rope holder. This feedback can be increased exponentially if the diver can see him or herself executing what was just attempted. A camcorder is invaluable, but A TIVO with instant replay can be worth another 30% for instant improvement. A knowledgeable coach or assistant can even hit play back on a TIVO and then move the device to slow motion. 
The only drawback or caveat is that only one person can be exercised off a tramp or dry land, whereas divers sharing a board can keep circulating. While the one diver is on trampoline or dry land, the others (if there are others) have to either sit and watch, or engage in other activities. So a busy trampoline and dry land set up should have other possibilities available, to keep the divers busy who aren't being held on the equipment.

"Other possibilities" include such things as pure strength and flexibility exercises. At the minimum, this can mean crunchies, leg lifts, chin ups, stretching, hand stands (free or against a wall), simulating take-off jumps, a "towel drill" for coordinating the speed of the arms with one's take-off squat and throw, etc. 
Under "Other possibilities" we should not forget that divers need quick reflexes and leg power. These aspects can be tended to by moderate distance running, quick 20 to 30 yard sprints, and even plyometric jumps.

Corrective Exercises: forward dive pike & somersaults

Re-edited 3/10/2001.

Problem: The diver has trouble with the forward category. The shoulders are generally too far back, or the body trunk leans too much to compensate for the shoulders being back. Analysis of the chain of cause and effect, shows that the diver has trouble working the board during the hurdle step, in order to come down on the end on balance with shoulder tips "in line." The shoulder tips are "in line," when the diver can land on the board with enough balance to set either the forward category or the reverse category with consistency.  

Solution: Several corrective exercises or planned movements may be helpful for "rehabilitating" such a diver.

1) The arm swing and eye change for forward take-offs should be studied and perhaps changed. For example, if the diver cant avoid falling off forward, before starting any kind of jump, the diver is perhaps leaning forward with the upper body during the descent of the jump to the end. The diver can also be looking at the board end too long, or looking at the water too soon, before any kind of upward action with the arms has pushed the board further down in preparation for the takeoff. 

2) A dry land simulation of the hurdle step should be practiced with acute attention to the length of the steps and the jump. Particular attention must be paid to making sure that the beginning, intermediate and advanced divers understand that the jump of the hurdle is being interrupted. That is why the hurdle jump is only marked off with two feet (instead of more length), whereas the last lead-up step is the most important and the longest step in the whole hurdle. How long should the long step be? That would take a whole article, so let’s be brief (and perhaps unfair) and suggest four units of the diver’s foot length. 

3) Working the board: This type of movement regularization can be experimented with, either on a trampoline or on a diving board. A trampoline is often best, because it always has the same rhythm, whereas diving boards do not always respond to a diver's movements in the same way. Even divers who do it are sometimes not even aware that it is part of their style. Others who try to learn it may find it too disruptive to their habits. The movement consists in pushing the board down with the ball of one’s foot in the step before the long step that starts the jump to the end of the board. On the first of the two steps, the diver attempts to place first the heel, then bend the knee and sink the weight with trunk erect over the heel and move it forward towards the ball of the foot. When the weight is starting to press on the ball of the foot, the diver gives a push to the board, while maintaining the body on a vertical but level plain (in other words with no big upward spring). Now, when the diver takes the next step, he must likewise get the heel (or flat of foot, but never the ball of the foot) down first and let the knee bend, so as to "go into it" the same way he did the previous step, with one exception: when the diver comes to the point where he merely pushed the board, this time the diver goes into his hurdle jump. The result hoped for is that the diver will have activated the rhythm of the board on the first step, so that when he goes into the second or hurdle step, the board will already be in the process of depressing and reacting upwards in synchronization with the diver's steps. This activation of the board's rhythm enables the diver to feel the board's rhythm more easily. When this is done, the diver can take advantage of the increased flexibility of the board, in order to depress it and then "ride" it as it reacts upwards during the diver's hurdle and following take-off from the board.  

This method is somewhat similar to the Greg Gunn technique (Princeton University age group diving), which I always thought looked a little like a “stork jump.” Some coaches and divers have worked out variations on this idea that work for some, but not for most.  

All that preceded can be nullified, if the diver does not take extreme care to be meticulous down to the inch and the centimeter when practicing achieving the proper length for each step and the hurdle. This can mean taking the eyes off the end of the board, where they normally should be focused, and watching each foot as it comes down on the board to match up the tip of the toes with the chalk mark that shows where the foot should reach. This idea should not be followed too much, since the diver may then take on the habit of looking down too much or too long, while executing a hurdle during a dive. 

4) When the diver has practiced the hurdle in the preceding manner on a trampoline, he should then switch to a diving board; and if he was first working on a board, he should then switch to a trampoline. The idea is to repeat the maneuver in a slightly different medium or movement situation, so as to add breadth of the diver's understanding (feel) for what is correct. 

5)Further corrective movement training can be done by practicing take-offs from the hard floor in the four different directions, and then on a trampoline or diving board. The idea here is not to execute a dive, but just to jump forward or back-ward with the proper type of range of motion and shifting of the weight from ball of foot to heel and back to ball of foot, while the arms and eyes move to the positions they should be at various points in the take-off.  It should be noted, of course, that there are four kinds of take-off, two forward and two backward. These could be reduced down to two, since the forward dive pike and all the forward somersaults start the same way as the inward dive pike and somersaulting category start: ie, the arms go up in a first movement (no matter how reduced in range of motion) simultaneously with the diver rising on his toes. The arms then sweep downwards and behind the hips at the same time that the heels should come down, with the upper trunk erect (or nearly so) over the heels. In the third movement, when the arms sweep up, the weight will be momentarily still over the heels on forward takeoffs. But in the fraction of a second when the arms optimally reach the highest point of the upward sweep, the diver must then pick whether to lean forward with the down-driving arms, or to pop the butt back and up with the down-driving arms. That is the fourth moment in the take-off, which we call "setting the dive."