"People loved him and really respected him," said Jason Viloria, the high school's principle. "He collapsed in classroom at lunch and discovered by students and a staff member."
Officials said a staff member performed CPR, but was unable to revive the 46 year old.
"I can't imagine how that feels, to be the one to have found him," said student Tess Iskra. "Everyone's grieving. A lot of the teachers are really sad. They were all crying."
"He was just such a great guy and all his students loved him," said another student, Quinn Boden. "I don't think there was one student who didn't like him."
Bentley was a teacher and coach for 12 years at Woodbridge, were he taught English and coached wrestling.
He's also remembered as an outstanding wrestler himself at Irvine High School.
Those who knew him said teaching was his calling. He belonged to three generations of teachers.
"His demeanor was one perfectly suited for a classroom, Viloria said. "He never got riled up, never got frustrated, always using everything as a teaching moment to work with kids."
Extra counselors are at the school to help students and staff with the grieving process.
"This is an iconic figure," Viloria said. "He was a mentor for so many students, so right now we're helping students process with the fact he's no longer here."
Authorities said an autopsy found Bentley died of natural causes. He showed signs of cardiovascular disease.
He leaves behind a wife and two daughters.