Prep School

Prep School is a miscellaneous quest in Fallout 4.

Detailed walkthrough
After completing Traffic Jam, Deb will tell the Sole Survivor 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 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, then attacking the caravans regardless. Kessler would like the player character to kill Zeller and eliminate the raider problem once and for all.

If a hard Charisma check is passed, Kessler will not raise the monetary reward. However, 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.

Judge Zeller and his gang are located in 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 other raiders killed, one 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. There is an alternative entrance directly to the third floor, which can be accessed by jumping from the remains of a crashed plane nearby, using jet or a jet pack.

Return to Kessler to receive the reward, namely 400 caps and the ability to build trade caravan posts at settlements. In addition to the reward, upon successfully turning in this quest, the caps inventory of the six main Bunker Hill traders (Deb, Kay, Cricket, Doc Weathers, Lucas Miller, and Trashcan Carla) increases by 300 caps permanently. This is cumulative with the similar 150-cap increase rewarded for completing Traffic Jam.

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. One can also type "completeallobjectives 0012221f" when talking to Kessler if the previous solution didn't work.
 * If any caravan survivors are killed before speaking to them (thus "rescuing" them for purposes of the objective), it will be impossible to update the objective and complete this quest.