By Mike DeNardo

PHILADELPHIA (CBS) — Philadelphia’s principals union — which rejected a contract agreement earlier this year — has elected a new president.

In June, the principals turned down a tentative agreement. Now, they’ve turned away their president for the last six years, Rob McGrogan.

Members of Teamsters Local 502 of the Commonwealth Association of Administrators have elected Longstreth Elementary principal Robin Cooper as their new president. Cooper says she was surprised her slate won.

“It was very grass-roots and we were in contact with a number of administrators,” she said. “But there was still a shock, that it worked so well.”

Cooper is a 24-year veteran of the school district — the last 18 as an administrator. She says members want to recoup wage concessions made in recent years, but they want to negotiate better working conditions, too.

“Over time, it was a loss of trust and the work intensified and the loss of money and the work conditions,” she said “So, it was everything.”

Negotiations were on hold until after the election.

Cooper takes office in January.