Updated

The headmaster of a suburban Philadelphia prep school who fought with his son over marijuana will return to his job after an assault charge was dismissed.

The Haverford School said Wednesday that the board of trustees' decision on the status of John Nagl followed an assessment of what was called "a deeply personal" family matter.

Nagl was placed on administrative leave after he was accused of assaulting his teenage son Oct. 10 in a dispute over a cellphone and marijuana.

Delaware County prosecutors filed but later dismissed a simple assault count, saying they had probable cause to arrest Nagl but "insufficient evidence" to pursue prosecution.

The school said Nagl had expressed "sincere regret." Nagl vowed to "personally reflect on how I can grow as a father and as a leader."