Prep School

Prep School is a miscellaneous quest in Fallout 4.

Detailed walkthrough
After completing Traffic Jam, Deb will tell the player to speak to Kessler, who also has a job to be done.

Kessler is looking for someone to discreetly remove Bunker Hill's raider problem. In the past, they've paid off Judge Zeller and his gang of raiders to leave their caravans - and the town itself - alone. Recently, though, Zeller's been demanding more money and then attacking their caravans regardless. Kessler would like the player to kill Zeller and remove their raider problem once and for all. If a hard Charisma check is passed, Kessler will not raise the monetary reward, but she will provide some extra ammunition, as well as 2 Med-X and 2 stimpaks. Even if the job is refused, the objective is added to the journal for the player to pursue.

Judge Zeller and his gang are located in the East Boston Preparatory School due east of Bunker Hill (across the water and just north of Boston Airport). The school has three floors and can contain anywhere from a dozen to 30 raiders. The self-appointed Judge Zeller holds court on the third floor, where he can be dispatched like any raider boss. With him and all of the raiders killed, the player is free to pick the locks on the three prison cells and free the caravan prisoners. They must be spoken to before they will actually start running out of their cells and the objective updates.

Return to Kessler to receive some rewards, namely 400 caps and the ability to build Caravan trading posts at the player's other settlements.

Bugs

 * If you previously cleared the location and decided to free the prisoners before accepting Kessler's quest, the miscellaneous quest item "rescue any caravan survivors" will still be on display after finishing the quest. The quest itself will finish and you will get the settlement item trading post and the quest will not show up if one uses "sqt" in the console.
 * If any caravan survivors are killed before speaking to them (thus "rescueing" them for purposes of the objective), it will be impossible to update the objective and complete this quest.