ZAHN: In tonight's eye-opener, a troubling syndrome that's tearing many children and parents apart is one that can be especially painful at times like Father's Day. While most kids were spending time with their dads yesterday, others went out of their way to avoid their fathers all together yesterday and experts say a growing number of children whose parents divorce are being taught by one parent that the other, in many cases, the father, is a monster. And the devastating results are detailed in this month's "Best Life" magazine. Jason Carroll has more in tonight's eye-opener.

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JASON CARROLL, CNN CORRESPONDENT: It is the end of another family get together at the Opperman home. These should be happy occasions but there are only bittersweet for Jeff Opperman. They remind him of a time before his contentious divorce, before he was alienating from his youngest son, a son who now wants nothing to do with him.

JEFF OPPERMAN, DIVORCED FATHER: I remember the child who would come get me at night when he had a bad dream. I remember the child who wanted to play baseball with me. That child doesn't exist anymore.

CARROLL: The last time Opperman saw his youngest son, he was 11 years old. That was six years ago. Now Opperman's only connection to him are through class photos, sent to him by his son's school once a year. His mother did not want us to show his face.

OPPERMAN: It is incredibly difficult for me. One day a year, when these pictures show up, I'm transported back in time and I relive the pain, all the anger, all the frustration of losing my child to parental alienation.

CARROLL: Parental Alienation Syndrome or PAS, some psychologists call it a form of brainwashing. It is what happens during a divorce when one parent deliberately destroys a child's relationship with the other parent, by bombarding the child with negative comments and feelings of hostility like in the Oscar nominated movie, "The Squid and the Whale."

CARROLL: It is not just in the movie. The author of a recent book on PAS says in real life it's deep rooted effects are felt by millions of children.

DR RICHARD WARSHAK, PSYCHOLOGIST: It as though they are developing the kind of hatred that people develop when they have a racial hatred, when they hate people just because they are of another race. They focus only on perceived negatives.

UNIDENTIFIED CHILD: I hated by dad, I hated myself.

CARROLL: For years this 17-year-old girl whose identity we concealed for her privacy believed her father wanted nothing to do with her after her parents' nasty divorce. She was just eight when her mother started telling her that her father never wanted to see her again.

UNIDENTIFIED CHILD: I thought he didn't love me. I thought he didn't want me anymore. I felt if my own dad didn't love me or want me, then who would.

CARROLL: But, when she got older and visited her father, she realized she had been lied to all of these years.

UNIDENTIFIED MALE: It really made me see that my dad couldn't be the person my mom was making him out to be. He was so loving.

CARROLL: So loving, in fact, she decided to move in with him and is much happier now. Those who have studied PAS say most children never return to the alienated parent.

WARSHAK: What is washed out of their minds are any memory of having a good relationship with the parent. They really act, in many ways, like victims of cults do.

CARROLL: Experts say mothers are usually the ones accused of PAS because courts typically grant them primary custody. Skeptics worry abusive fathers will use PAS against mothers to gain access to their children or to avoid child support payments.

DR. AMY NEUSTEIN, SOCIOLOGIST: The PAS label sticks to the mother like glue. And that's very, very dangerous.

CARROLL: As in many difficult divorces, the two sides in Jeff Opperman's case disagree. A Superior Court judge said both parents bear some responsibility for the dilemma, but the judge in the case also said the court believed that the main responsibility rests with the wife, who allegedly sent the son wrong messages about his father. Opperman's ex-wife told CNN she didn't bad mouth him and encouraged her children to have a relationship with their father, adding Opperman is being vindictive. Opperman is thankful for now to have a relationship with his older son.

GREG OPPERMAN, CHILD OF DIVORCE: It was like I was trying not to play favorites and there is a lot of pressure to be someone's favorite.

CARROLL: On June 5, Opperman reached out to his son again. This time he sent an email. It reads: "I'll always be your dad no matter how old we get. I'll love you and miss you."

The response like the others over the years.

OPPERMAN: That's what happens. Not read.

CARROLL: If he does choose to respond, he says that he will be there for him. Jason Carroll, CNN, Fort Lauderdale, Florida.

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ZAHN: Tough road ahead there. Another thing we would like to add is a thank you to our friends at "Best Life Magazine" for their help in getting this story on the air.