As you said, through schooling. If a person chose all stifle dogs to school his charge and then on show night he experiences his first head dog he will be in trouble. He will not have the ability and/or knowledge to figure things out. Some dogs have natural ability and talent and figure things out quickly but it is the owners responsibility to provide him with as much experience in all areas to enhance that ability. In some cases ability and experience go hand in hand and are one in the same.
If a dog lacks ability and can't wrestle he should be exposed to another who will help him get there. After that exposure even if the ability is not where one would hope for it will still be better (enhanced) than it was in the beginning. Easier said, ability is enhanced through experience and for the dogs that experience is through schooling. Of the things that one can enhance ability is the easiest. EWO