Three boys were attacked in separate incidents in the classroom of teacher Emmanuel De La Rosa at A.B. Miller High School, Fontana police Sgt. Robert Morris said.
One 18-year-old student - Fernando Salgado - is being investigated for child cruelty, assault with intent to commit mayhem or rape and attempted sodomy. Salgado is due for arraignment Tuesday.
De La Rosa, 27, may have directed the students to carry out one of the assaults, Morris said.
"They would assault the other kids to basically maintain order in the classroom on their own," Morris said. "The teacher at some point became aware of the situation, and knew about what was occurring and in one incident may have actually directed them to do it."
One of the victims suffered minor injuries. Morris declined to detail the nature of the assaults, citing the ongoing investigation.
De La Rosa was arrested Saturday for investigation of child cruelty and has been placed on administrative leave. Three other students arrested were minors.
De La Rosa, who was released Sunday, could not be immediately reached for comment. Nor could Salgado, who is being held on $100,000 bail.
Salgado's sister, Krista Hernandez, said police came to her house over the weekend looking for her brother. She found him with friends and they went to the police station together to see if they could answer officers' questions when he was arrested.
Hernandez, 28, said he was in shock when she told him about the allegations Monday.
"He started to cry to me saying he didn't do these things, and all he wants is to come home," Hernandez said, adding that he needs to finish coursework during summer school to graduate from high school.
Hernandez said she believes the allegations will eventually be dropped against her brother and speculated they might stem from horseplay that got out of hand when someone got hurt.
"He's definitely a jokester, he's definitely someone who might mess around here and there, crack jokes in class, probably things a lot of kids do but nothing in the nature of what they're saying," she said.
The probe began Friday when a victim reported one of the incidents to the Fontana school police, who referred the case to the city's police department.
The school has assigned an assistant principal to take De La Rosa's place for the last week of a five-week summer session, and professional counselors have been sent to the campus about 50 miles east of Los Angeles, said Fontana Unified superintendent Cali Olsen-Binks.
"We're all taken aback, most definitely," she said, adding that the teacher was very popular with students at the school.
De La Rosa, a trained bricklayer, did his apprenticeship and worked at Winegardner Masonry in the nearby town of Yucaipa, said Julie Salazar, the company president. He left the company four years ago to become a teacher, she said.
"He always was a respectful person, so it comes as beyond a shock," Salazar said. "That doesn't reflect anything at all about how we knew him here."
No charges had been filed in the case as of Monday. De La Rosa was expected to appear in court Wednesday, said Christopher Lee, a spokesman for the San Bernardino County district attorney's office.