The valedictorian of a Brooklyn high school was escorted out of the building and denied her diploma yesterday because she trashed the school in a scorching graduation speech. The school says it won't give Tiffany Schley her sheepskin until she says she's sorry - but the 17-year-old is unrepentant. "I was speaking for my peers," Tiffany told the Daily News. "We've been living with this for four years."

A top student who's going to Smith College on a full scholarship this fall, Schley was brutally honest about the High School of Legal Studies during Thursday's graduation ceremonies in Bushwick.

Among her gripes: The school has had four principals in four years, overcrowded classes, a shortage of textbooks and other basic materials, unqualified teachers, unstable staffing and uncaring administrators who refused to meet with students to discuss the school's problems.

"They always want to keep the problems hush-hush, but what goes on in this school is real," said Tiffany, who was also the editor of the school newspaper, yearbook chairwoman and a member of the student council.