JACKSONVILLE, Fla. -

An investigation failed to turn up causes for extremely high numbers of erasures on last year's Florida Comprehensive Assessment Test at four schools, state education officials said in a report released Friday.

The report says investigators did find that two teachers at Greensboro Elementary School in rural Gadsden County had coached or interfered with student responses on the 2011 FCAT, but evidence did not indicate teachers altered students' responses at any of the schools.

The Department of Education's inspector general's office also investigated high numbers of erasures at Chaffee Trail Elementary School in Duval County, the Charter School of Excellence in Broward County and Jefferson County Elementary School. The Florida Department of Law Enforcement also participated in investigations at two of the schools but found no criminal wrongdoing.

"In all four schools, multiple individuals had custody of a key to the secured room where the test materials were stored during the two week administration of the FCAT," the report noted.

It recommended several changes to ensure FCAT security including that no more than two people have access to the locked storage areas. The report also said the amount of time one person is left alone with secure materials should be minimized and that two people should be present when materials are unpacked, prepared and packaged for return to the district office.

The two teachers accused of coaching or interfering at Greensboro refused to be interviewed by the inspector general's investigators. The school's principal and guidance counselor told investigators they were unaware of any coaching or interfering.

The standardized test is used to grade Florida's schools. Jefferson Elementary ultimately received an incomplete because the department was unable to evaluate its accountability based on available data. The other three schools, though, received grades of "A'' last year.

The investigation was launched after an analysis used for the first time found anomalies including an extraordinary number of erasures at 21 schools. School districts then conducted internal investigations, which the department used to conclude any advantage of irregularities was minor in 17 districts. Also, no improprieties were identified in those districts.

The department asked the Florida Department of Law Enforcement to jointly investigate Jefferson Elementary as altering or interfering with the FCAT is a criminal violation. FDLE issued a report in December saying it was unable to determine the cause of the erasures.

For the other schools FDLE asked education officials to notify the agency if they found any suspected criminal activity. FDLE subsequently conducted an investigation at Chaffee Trail, where in March it reported finding no criminal wrongdoing. FDLE did not participate in investigations at the other two schools.