Baltimore County school spokesman Charles Herndon said Phelps will be a director for the Education Foundation, an organization that seeks help from the business community to raise money for schools.
Phelps was not available for comment. She posted a letter on the school website Monday night saying that she was grateful to have had the opportunity to work with students, parents and staff for the past six years.
The assistant principal, JoAnn Rich, will take over as acting principal of the school near Randallstown until a new principal is chosen. A letter posted on the school's website says that meetings will be held Thursday with parents and staff to gather information about what characteristics they believe would be important in a new principal.
Windsor Mill Middle School has been labeled a failing school because of low student test scores. Under the federal No Child Left Behind law, Windsor Mill would have had to be overhauled this summer, but because the state got a waiver from the law, those plans are no longer required.
Dance said he would evaluate whether the schools should go ahead with the plans that were presented to state officials and approved. It is not unusual for the principal to be moved when a school goes through a restructuring.
Dance said he believed the foundation had been stagnant for the past several years and needed a full-time staff person to further its work.
He said he approached Phelps, asking if she was interested in the job. "She was extremely receptive," he said in a text message.
"I think it is a great move for her," said Joshua Parker, a Windsor Mill English teacher who is the state's teacher of the year. "She gets a chance to talk to business heads in the community. I think that is a natural fit for her."
Though the school met its targets for test scores this year in reading, he believes more progress is needed in math. He said the school will benefit from fresh ideas.
An earlier version of this article misspelled Joshua Parker's name. The Baltimore Sun regrets the error.