The principal of East Ridge High School in Woodbury resigned Thursday after becoming the focus of an investigation prompted by a complaint to the school district, district officials said Friday.

The South Washington County school board accepted the unconditional resignation of principal Aaron Harper at its meeting Thursday. The resignation was effective immediately.

Harper was not immediately available for comment Friday, nor was school board chair Ron Kath.

Harper had been placed on administrative leave after undisclosed allegations were made against him, said district spokeswoman Barbara Brown.

Brown would not discuss the nature of the allegations nor say when they were made. She said that they were not being disclosed because no disciplinary action had been taken since Harper resigned after the investigation was completed.

Brown said the district did not offer Harper any payment in exchange for his resignation and that Harper had acknowledged that the district had treated him fairly.

Harper has been the principal at East Ridge since it opened in 2009. He started with the district in July 2006, when he was hired as the principal for Oltman Middle School. After a year at Oltman, he was selected as the principal to lead the construction and opening of East Ridge.

The school district will retain an interim principal for the remainder of the school year and will start a national search for a replacement in January. Mike Johnson, an assistant superintendent, will help the East Ridge administration until an interim principal is named.

Nicole Norfleet • 612-673-4495

Twitter: @stribnorfleet