OAKLAND -- A weekend burglary at East Oakland PRIDE Elementary School turned dozens of classrooms upside down and cost the schoolchildren a day of class.

School was dismissed Monday morning after school staff members discovered that 30 classrooms had been ransacked, Oakland school district spokesman Troy Flint said. Among the items stolen were a safe from the principal's office, document cameras and Mac computers from the school's newly refurbished computer lab.

Jacqueline Calderon, a second-grade teacher, said she was on her way to work Monday when one of her colleagues called to tell her about the break-in. She said she first saw the wood chips covering the floor of the principal's office, from his door being smashed in. Then, along the upstairs hallway, she noticed all of the glass -- "protruding shards of broken glass."

Flint said school police officers are investigating the break-in. He said he did not think the alarm was triggered.

Burglaries and vandalism occur with alarming regularity in the district's schools. One school, Sobrante Park Elementary, sustained a series of arsons during the 2008-09 school year. Adam Taylor, principal at Brookfield Elementary School, estimated last year that his school had been broken into at least 25 times in 18 months.

East Oakland PRIDE was burglarized at least once this school year, during the Thanksgiving holiday, and once last summer.

On Monday, school staff cleaned up broken glass -- windows had been smashed in about every classroom -- figured out what was missing and tried to restore a semblance of order.

"We're just really surprised by how big of a job it was, how expensive it was and how much they took," Calderon said. "We're wondering, how did they have so much time to carry so much material without anyone noticing?"

The school is located on the old Webster Academy campus at 81st Avenue and Birch Street, near Arroyo Viejo park. It opened in 2007 as part of a school district initiative to create small, successful schools in some of the city's most troubled neighborhoods.

To report information about this incident, call Oakland schools police at 510-874-7777 or e-mail police@ousd.k12.ca.us.

Staff photographer Laura A. Oda contributed to this report. Read Katy Murphy's Oakland schools blog at IBAbuzz.com/education. Follow her at Twitter.com/KatyMurphy.