Over time they start to grant each other "rewards" for being able to name the shadows the quickest. This relates to the classroom in the form of grades and the student that gets the most shadows correct has the highest grade. Life in the cave seems like a simple life because all the prisoners have to do is know which shadow is which to receive some sort of reward, but what happens when one of the prisoners is released. .
A prisoner getting released is the start of "turning the soul in the right direction" in Plato's Theory of Education. If a prisoner got released, the first thing that would happen is his "Educator" that released him would turn him around and show him the fire and say the shadows are just an illusion. He would be blinded by what he now thinks is the actual truth. It would take the freed prisoner a while to understand how the shadows are casted and then realize that the educator is correct that the shadows are in fact illusions and not the real thing. The man that released him now drags him to the surface and they ascend out of the cave. This would relate to a teaching style that can be found in some classrooms where the professor makes the students think and figure out the answer instead of just telling them what the answer is. This helps the students gain a better understanding of the answer and why the answer is what it is. It would be a lot easier for the professor to tell his students the answer, but taking the harder route and trying to pull the answers out of the students is what truly gets them to learn.
Once the man that released the prisoner brings him out of the cave, the "turning of the soul in to the right direction" has been complete. The "Educators" part is done. It is now the prisoners' turn to learn for himself and formulate reason. As soon as he gets out of the cave, the sun blinds him. He can't see anything because the sun is brighter than anything he has ever seen.