"Simply put, I want to redirect more of my time and energy toward my children, my grandchildren, and my career," said Ritter, who would have been up for reelection next year.
Ritter cited his work schedule and the heavy time commitment the district has needed from its school board members over the last few months - and will need in the future - as reasons for his resignation.
Ritter, executive vice president and chief operating officer at the New Jersey-based Cumberland Insurance Group, said he was going away on business and would have missed board meetings.
The school board has 30 days from the time of the vacancy to vote on Ritter's replacement, according to the Pennsylvania School Code. Ritter represented Caln and West Brandywine Townships.
He said in his letter that he regretted not having the opportunity to work with the new superintendent, Cathy Taschner, who officially started a month ago.
Taschner replaced Richard Como, who resigned last year after the school district discovered racist and sexist text messages about students and staff that he exchanged with athletic director James Donato, who also resigned.
Ritter came to the board in 2007 and was reelected in 2011. He served on the finance committee and was a former vice president of the board.