I believe that Ralph changes drastically during his stay on the island. He does not start out as mature--in fact, every time he becomes excited about being alone on a "good island" without adult supervision, he can't even find the words to express himself, so he stands on his head to express his enthusiasm, which is quite immature.
He is certainly not accepting and tolerant at the beginning, either, as he appears to be quite prejudicial against the fat boy with thick specs named "Piggy." He tries to sneak away from Piggy at first, but then, realizing that Piggy will not be left behind, Ralph grudgingly puts up with his company. After Piggy asks Ralph not to tell the others of his humiliating nickname, Ralph goes right ahead and tells them anyway (again displaying the immaturity he arrives with on the island). Noble at this point is out of the question.
Ralph tries to be somewhat responsible up to a point, but he's not that interested in responsibility--that is Piggy's forte. A list is supposed to be made of all the kids on the island, but it does not come to fruition. Then there is the fire on the mountain, and the boy with the mulberry birthmark is killed--and they can only account for his death because of the noticeable birthmark. This is when Ralph takes a more serious turn.
As the other kids lose their sense of civilization, Ralph tries more and more to be responsible and noble, even though he, too, at times, lapses, such as in the killing of Simon.
The traitorous and violent turn that Jack takes makes Ralph very fearful for the boys who are still on his side and for himself, especially at the end when he is being hunted. As they are rescued, this fear has its catharsis in the weeping that Ralph is finally able to give in to.