After only 17 months on the job, Jeremy Nowak has resigned as president of the William Penn Foundation in what the Philadelphia Daily News described as a culture clash between the forceful, publicly prominent executive and low-key board. Penn officials said the foundation remains committed to the strategic plan developed on Mr. Nowak’s watch and unveiled in July, which has seen the organization take a leading role in local school-reform efforts.

In a statement, the foundation attributed Mr. Nowak’s departure to “differences in approach” in implementing the plan, under which the $2-billion fund will spend $80-million a year supporting educational, environmental, and cultural causes in the Philadelphia area.

Brent Thompson, the foundation’s communications director, said the change is “about style, not substance” and that a presidential search is under way. Helen Davis Picher, a veteran Penn official currently serving as director of evaluation and planning, will act as interim president.