A former Bucks County high school teacher who had a five-month sexual relationship with a 17-year-old student - with the apparent knowledge of his peers - was sent to prison yesterday.

Robert C. Hawkins, 43, a once-revered math teacher at Council Rock High School South, was sentenced to 111/2 to 23 months in the county prison.

But Hawkins was led away with his lips still sealed about which of his former colleagues knew of the illegal affair and said nothing.

Two teachers have been fired and a third has resigned in the probe. Hawkins so far has refused to speak to investigators, Deputy District Attorney Jennifer Schorn said.

Hawkins pleaded guilty Nov. 18 to endangering the welfare of children and corrupting the morals of a minor. He was fired in May after the relationship was revealed.

Beginning in December 2008, he and the female student began having sex in Hawkins' Newtown home three or four times a week. He was not charged with sexual assault because the victim was over 16 - a consent law that Hawkins had the girl research herself in an effort to gain her cooperation, authorities said.

"I don't mean to be crude," Bucks County Court Judge Clyde W. Waite told Hawkins. "But the manipulation and isolation of impressionable young people is pretty much what a pimp does."

The judge also had harsh words for teachers who submitted letters seeking mercy for Hawkins. "The seriousness of what you have done is accommodated by them, and I don't think it should be," Waite said.

The judge also said he might reconsider Hawkins' sentence if the former teacher cooperated with the investigation into colleagues who failed to report his crimes.

Council Rock Superintendent Mark Klein called Hawkins a "self-centered predator" and expressed disappointment that some district teachers would support him. "The vast majority of our staff is outraged by Mr. Hawkins' actions," he said.

The victim's father said his daughter had been a friendly, unsuspecting straight-A student, a "perfect daughter . . . who breezed through life."

He said Hawkins had begun targeting her for abuse in the 10th grade, paying special attention to her and even befriending her parents as a means of grooming her.

By the time Hawkins' abuse began, the father said, "she was under the control of this manipulative and cowardly teacher." Now, he said, the girl "is in a splintered emotional state."

Hawkins "changed who she was," the victim's mother said, leaving the girl unable to trust others. "The damage is deep, and will likely affect our daughter for the rest of her life."

Hawkins' lawyer, Marc Neff, called his client "multidimensional" - a talented and inspiring teacher who failed to set appropriate boundaries. "Those accomplishments do not go away because he fell down on the job on this particular occasion," Neff said.

In court, Hawkins said he had made choices "that were completely wrong and reprehensible. . . . I am ashamed, sorrowful, and guilt-ridden."

He drew glares from the victim's father and sobs from her mother when he claimed he had meant no harm.

"I truly believed that we had fallen in love," he said.

But Schorn said Hawkins' behavior was not unprecedented. The year before, he had engaged - legally - in a sexual relationship with an 18-year-old student as soon as she had graduated, she said.

Waite could have placed Hawkins on probation, but said prison time would underscore the seriousness of his betrayal of community trust.

The sentence "sends a strong message that his reprehensible conduct will not be tolerated," the victim's parents said in a statement afterward. "As parents, none of us should have to worry that when we send our children to school they will be preyed upon by their teachers."

Contact staff writer Larry King at 215-345-0446 or lking@phillynews.com.