Source : Webster's Revised Unabridged Dictionary (1913)

Valedictorian \Val`e*dic*to"ri*an\, n.
   One who pronounces a valedictory address; especially, in
   American colleges, the student who pronounces the valedictory
   of the graduating class at the annual commencement, usually
   the student who ranks first in scholarship.

Source : WordNet®

valedictorian
     n : the student with the best grades who delivers the
         valedictory at graduation [syn: {valedictory speaker}]