Have a look at Mother, Any Distance, by Simon Armitage, or Teenage Sky, by Rosa Adshead.
Both of these poems engage with the difficulties of growing up and the changes that occur as one gets older. They clarify their key idea or concerns in the closing lines.
In Mother, Any Distance, the persona is grappling with the difficult process of growing independence and the distance that this necessarily creates from his mother. The key phrase "Anchor. Kite." Captures the figurative image of both distance, but also strong connection. The final lines resolve this central concern by admitting that the persona is stepping up and out into an unknowable future, and connects back to the image of anchor and kite by admitting that he may 'fall' or 'fly'. The final lines are effective because they show that, when it comes to growing up, certainty of success is sometimes not as important as giving new things a go. What matters most is that you have a strong connection with others - especially parents.
In Teenage Sky, the poet uses an extended metaphor to compare some experiences of adolescence with the changes that take place at the start of the new day. She uses figurative imagery to show that awkwardness, embarrassment and change are normal, and, in their own way, beautiful. The final lines of the poem are effective to the central concerns of the poem because they show that this is a message of hope: the poet promises that one day, despite all of the present difficulties, the adolescent will feel bright with fulfilment, just like morning eventually reaches the brightness of noon.
I hope that helps and good luck with the assignment!
"Richard Cory" [http://www.poetryfoundation.org/poem/174248] by Edward Arlington Robinson is a poem in which the reader encounters the revelation of the hidden heart of the man named in the title only with the last line.
Set in the Depression of 1893, when the common people were starving, and would, indeed, look up "from the pavement" in envy of one as wealthy as Richard Cory, there would be no concern for Cory's psychological state because these poor people would feel that this gentleman had no reason to be unhappy. Instead, they view him as king-like and apart from them in every way. So, it not until the very last line of the poem that the theme and message of the poem are revealed.
In his novel A Tale of Two Cities, Charles Dickens reflects in one of the early chapters entitled, " The Night Shadows,"
A wonderful [meaning cause for wonder]fact to reflect upon, that every human creature is constituted to be that profound secret and mystery to every other...that every beating heart in the hundreds of thousands of breasts there, is, in some of its imaginings, a secret to the heart nearest it! Something of the awfulness, even of Death itself, is referable to this.
This passage of Dickens could well describe Richard Cory, who for all his "imperial" slimness and politeness and perfect smile and "glitter when he walks" as though a being supreme, surprisingly, "went home and put a bullet through his head." Indeed, no one of the townspeople is at all aware of Cory's "imaginings"; not one of those who "cursed the bread" that was their meager meal as they enviously dwelt upon Cory's repast of fine food knew the "mystery" and "imaginings" contained in the secret passages of his agonizing heart.