On the eve of a ballot initiative campaign aimed at raising billions of dollars for schools, the man who led the state's powerful teachers union for five years has resigned abruptly.

Richard Sanders, executive director of the Oregon Education Association, announced his departure this week.

The teachers union has been a driving force behind the Our Oregon ballot measures, which seek to raise the minimum tax on businesses with sales in excess of $25 million and thereby raise $2.5 billion.

The union is a major force in Oregon politics; traditionally, no entity has given more campaign donations to elected leaders in Salem.

Schools and teachers also represent the largest expenditure in the state's general fund.

Sanders will continue to advise the union to ensure a smooth transition, said union president Hanna Vaandering in a statement.

"We are extremely grateful for Richard's vision and commitment to OEA, and we wish him only the best," she said. "Richard truly set in motion a member-led movement within OEA which will remain a guiding principle of our work."

Sanders came to Oregon from Massachusetts, whose schools lead the nation. In a WW cover story last year, he praised innovation and cooperation in Oregon schools, saying he's never seen better in the nation.

"In this state, educators know what works," Sanders says. "We just don't have the money to do it."