What are some significant changes that Ralph from Lord of the Flies experiences in his journey to adulthood ?

At the start of the novel, Ralph has two outstanding traits that change during his experiences on the island.  The first thing we notice is that he is a little conceited toward Piggy.  Ralph seems to instantly determine that Piggy is socially inferior to him, and he acts superior to the asthmatic, overweight boy. We see this as Piggy talks quite a bit when they first meet, but Ralph tries "to be offhand and not too obviously uninterested" as he walks away (8). He won't bother to ask Piggy's name, and laughs at him when the socially awkward boy admits his unflattering nickname. Ralph even tells the other boys the nickname, betraying Piggy's secret.  

Ralph also has a great deal of confidence at first, not only in himself, but in the societal rules that adults have taught him and the other boys.  Ralph has no doubt that if they make rules and he leads they boys, they will form a civilized society that can work towards getting rescued. He believes in the adult ways and strives to emulate them.

However, as Jack and his tribe work to undermine the rules and Ralph himself, the young leader finds his self confidence slipping.  In chapter five, after Jack has completely disrupted and dissolved the meeting, Ralph tells Piggy and Simon, "'I ought to give up being chief...We're all drifting and things are going rotten.  At home there was always a grownup'" (93-94). 

At this same time, Ralph is learning to appreciate Piggy's helpful intelligence and honest friendship.  While preparing mentally for the meeting to set everyone straight and enforce the rules, Ralph admits to himself that he doesn't have the brains that Piggy does.  He realizes that his friend, "for all his ludicrous body," has the ability to logic things out like an adult (78). His hard life on the island has caused his childish conceit to melt away into a more adult set of social values.

The trouble is, no matter how they try to reason with Jack's tribe in an adult manner, the hunters continue in their downward spiral into savagery.  When Roger murders Piggy, shattering the conch, the last vestiges of Ralph's confidence in the adult system shatter with him. As the savages stage a full-on hunt to kill him, Ralph hides "among the shadows and [feels] his isolation bitterly" (185). He wrestles with his confusion about why things fell apart and how they can hate him so much. He determines that it's "'cos' I had some sense'" (186). The jaded young would-be leader faces the fact that the adult world is flawed too; creating a logical set of rules is not enough to control the evil that lurks in some people's hearts, nor the beast, or fear, that causes others to lose their moral values. 

In the end, as the Naval officer stands over him unfeelingly, Ralph weeps "for the end of innocence, the darkness of man's heart, and the fall through the air of the true, wise friend called Piggy" (202).  Ralph will be forever changed, and in his heart he realizes that his return to the adult world is truly not a rescue at all.