Episode 80 of "Boston public"
s04e14 Chapter Eighty

A former student of Winslow High dies in Iraq while serving the U.S. Army. Principal Harper receives a letter from the deceased student which brings back old memories back to the days when he took care of him and pulled him away from a life in the gutter. Danny Hanson struggles with a student in his class who's been hacking into the school's computer base... finding out about the teachers' private lives and upcoming tests.