NEWBURYPORT — More than 75 students used toilet paper, shaving cream, contraceptives and, reportedly, a flounder, to decorate the high school last night in defiance of the administration's warning on the traditional April Fool's Day senior class prank.

Police responded to the high school about 7:30 p.m. for reports of vandalism but did not arrest anyone, according to students at the scene.

About 90 students on Friday staged a sit-in after Principal Michael Parent informed seniors he would not accommodate the class's planned prank, in which they planned to be called to the auditorium and allowed to watch movies for part of the day. In previous years, classes have been allowed into school early on April Fool's Day to set up their idea.

Principal Michael Parent, Senior Class adviser Aileen Maconi and other staff watched from inside the school as students in the chilly drizzle outside toilet-papered trees and shrubbery, soaped windows, shaving-creamed obscene images on walls and wandered around the grounds. There was a barrage of snowballs, and one student said he threw a flounder onto the overhang above the main entrance.

Students were not allowed in the building, Maconi said, and she and other staffers made sure the rowdiness did not get out of control. Profane chants were tolerated, but Maconi immediately went after students throwing snowballs at windows.

"Most of this is innocent, but some kids go too far," she said.

Instead of snowballs, students adorned the door with contraceptives and feminine products before retreating to the driveway and front yard. Most students congregated in small groups and milled around the front of the school, carrying rolls of toilet paper or other pranking supplies.

Police reports over the radio said Parent later ordered students to leave school grounds about 9 p.m., saying they would be charged with trespassing if they returned.

Students at the scene said they had been told they could participate in a prank outside the school from 6 to 10 p.m., but Maconi said that was a rumor that had started at an assembly Friday, and was not school policy. The Friday meeting led to a student sit-in after Parent told students their planned prank — a senior movie day — was unacceptable.

Parent had initially approved the prank, but decided against it after talking with department heads. He also told students he would not open the school early on Tuesday for the traditional hijinks, as opposed to previous years. The announcement led to a sit-in at the assembly, with initially 90 students refusing to go back to class. About half of the students eventually returned to class over the 90-minute sit-in, but students in general were angry at the decision to revoke the prank.

"Students were really outraged," senior Tim Seely said on Friday. "A group of seniors had been talking to the faculty about the plan, and it was supposedly OK'd."

A rumor at the assembly suggested that students would be allowed to perform their prank outside the school, Maconi said.

"(Parent) told us we could do things outside of the building, though he will not condone anything disruptive and nothing can be done which is derogatory to a class or individuals," senior Michelle Bradbury said on Friday.

Maconi said students were "choosing to hear what they want" in assuming they had permission to perform a prank last night, but also said the situation was "mishandled." The decision to call off the planned prank came on short notice and led to confusion and anger, she said.

But Maconi said the school was trying to make sure no one was hurt during escalating pranks.

"It gets to the point where you have to one up and one up," she said. "Destruction can happen and people could be injured."

However, the cancellation of the first prank led to last night's vandalism, said student Becka Quarantiello.

"We told them that if they take away the prank, there would be consequences," Quarantiello said. "They didn't believe us."

Quarantiello said last night's prank had gotten "out of hand," though.

Student Teddy O'Connor said the original prank, where seniors would be allowed to watch movies while the rest of the school had to go to class, was more in line with pranks of the past that focused on uniting a class of students.

Quarantiello agreed, saying her grade wanted to live up to a pirate-themed prank of 2006.

"(The '06 class) had a lot of spirit, but we're not going to have that," Quarantiello said.