Socrates uses the allegory of a horse trainer to explain that he is a trainer, rather than corruptor, of the youth (Cavalier, "Ancient Philosophy"). Socrates' second argument in his defense is that, had harmed the youth, the philosophy that evil begets evil would dictate that the youth would harm him in turn. Being a believer in this philosophy, Socrates would be harming himself knowingly by harming the youth.

Regarding the charge of impiety, Socrates argues that he is in fact a guardian of the piety of the City. He has devoted his life to understanding divinity and in service of the gods. However, being disturbed by hearing the truth from Socrates, those indicted by his very piety accused him of impiety.

All of the accusations against Socrates therefore tend not only towards the hysterical, but also demonstrate the guilty conscience of the accusers. Their accusations reflect...

Seeking the death sentence for Socrates is not so much from a belief that their accusations are true, but rather that they want to be rid of Socrates and his indictments of them.
In the end, the accusers succeed in their goal to sentence Socrates to death; however, his response to both the charges and the sentence leaves the reader with the sense that Socrates has the ultimate victory. He maintains an air of not only composure, but also wisdom and acceptance, even towards his accusers and murderers. This, more than any verbal argument, proves Socrates' sincerity, piety, and innocence.

References

Cavalier, Robert. "Ancient Philosophy." http://caae.phil.cmu.edu/Cavalier/80250/part2/ApologyAnalysis.html

Plato. Apology. Retrieved from http://classics.mit.edu/Plato/apology.html