Dean Dewey is now the head disciplinarian, programmed to fill the role of Principal at the Roosevelt Academy. It is programmed to patrol the halls, making sure students are not in the halls without a pass. Much like other robots encountered in Fallout 3, Dean Dewey is apparently unaware that the Great War has occurred and will go about its schedule as if activated.
The Lone Wanderer can activate Dean Dewey by hacking the Headmaster's terminal. Subsequently, he will wander the corridors and attack any hostiles. If he challenges you for a hall pass, then you can use either the Child at Heart or Robotics Expert perk to talk your way out. If your Intelligence is 3 or below, then you will be called a "special needs" child and be escorted to a classroom.