But students shouldn't expect canceled or delayed classes.

"School is scheduled to start at the usual time," said Elaine Baker, school district spokeswoman. "We are optimistic that it will be a normal school day everywhere in the district."

A message left on a restroom wall last week threatened principal James Blake while another message targeted blacks and included a threat for today. On Thursday, new threatening writings were discovered, Blake said.

As a safety precaution, officials will step up security today at the school, normally monitored by one resource officer.

Before students were dismissed Thursday, Blake's intercom message addressed security concerns and sought campuswide support.

"Tomorrow, I will be here as I am every day," he said during the message. "I have your back as I hope you have mine."

Blake said the school district has earmarked money to purchase cameras for installation near restrooms and other areas not highly visible for adult supervision. The cameras, he said, are to be installed at Northwestern by the fall.