Police spokeswoman Monica Munoz said the San Ysidro High School students obtained a copy of the school's master key and snuck onto campus after midnight Tuesday. They stacked the desks and chairs in the hallway and put several pieces of furniture on a field in the shape of "09."
Their activity triggered motion sensors, prompting the school's alarm company to call police. The school, in a San Diego neighborhood about two miles north of the Mexican border, has about 2,200 students.
Police cited the students who were 18 years old for trespassing, and those under 18 for curfew violation. All of them were ordered to move the furniture back where it belonged.
Copyright 2009 The Associated Press.