WASHINGTON, Dec. 26 (Xinhua) -- A school in the south central U.S. state of Oklahoma has been sued under accusations that 15 elementary students were molested by a 86-year-old, the Associated Press reported Monday.

The federal lawsuit, filed on Friday, seeks compensation from the Perry school district and the school board for allegedly failing to protect the girls from sexual assault by Arnold Cowen, aide of a teacher.

Cowen has pleaded not guilty to some 20 charges, which include committing indecent acts to a child under 16.

This is the latest in a series of sex abuse cases in the country's numerous schools, which had long been plagued by sexual assaults.

Last week, a U.S. national charter network KIPP Academy released a report on accusations of sexual misconduct by two teachers after two alumnae said they had been abused more than a decade ago, according to an earlier report by the New York Times.