By Juan Perez Jr.

Barbara Byrd-Bennett has resigned as chief executive of the Chicago Public Schools amid a federal investigation into a $20.5 million no-bid contract.

In a letter dated last week, Byrd-Bennett said she planned to step down Monday. She did not give any reasons for her decision.

Byrd-Bennett has been on paid leave since mid-April, when school officials released wide-ranging subpoenas from the federal investigation. Her paid leave was scheduled to end next week and she had not been expected to return to her post.

The investigation centers on a $20.5 million no-bid contract at CPS related to an elite nonprofit education group that has long been at the center of city school reform efforts. Federal corruption investigators have also sought records related to some of Byrd-Bennett's top deputies.

Byrd-Bennett, who has not been accused of wrongdoing, acknowledged when she went on leave that her presence could divert attention from the pressing affairs of the district as it tackles labor talks with the city's teachers union and confronts a $1.1 billion budget deficit. In 2013, according to CPS records, the district approved a "leadership development services" agreement with the Wilmette-based SUPES Academy for up to $20.5 million that extended through June 2016.

District records show SUPES was hired on a "non-competitive basis" to train school network chiefs and principals. Byrd-Bennett once worked for SUPES.

Board member Jesse Ruiz, who took over when Byrd-Bennett went on leave, will continue to serve as interim CEO, according to a statement from board President David Vitale.

In her resignation letter, Byrd-Bennett said she will "remain forever thankful for the opportunity to serve the children of Chicago."

Mayor Rahm Emanuel released a statement saying he was "saddened by the circumstances that have led to Barbara's resignation and I wish her well."

(c)2015 Chicago Tribune