DEDHAM, MASS. -- A 15-year-old youth who beat a classmate to death with a baseball bat because he wanted to find out what it was like to kill someone was convicted of second-degree murder yesterday and sentenced to life in prison.

Rod Matthews, who was 14 when he lured his victim, Shaun Ouillette, into the woods with a promise of fireworks, was expressionless throughout the weeklong trial and when the verdict was read. He will be eligible for parole in 15 years.

Jeanne Quinn, the victim's mother, said she had hoped Matthews would be convicted of first-degree murder and therefore ineligible for parole. "Shaun is not coming home in 15 years, is he?" she said.

Matthews' family, including two sisters and a brother, was escorted out of court by a phalanx of officers. Kenneth Matthews, the father, said he felt his son belonged in a hospital rather than prison.

Defense attorney John Philip White had argued that Matthews should be acquitted by reason of insanity, portraying him as a mentally unstable child whose pleas for help were ignored by teachers and friends. White contended he had been adversely affected by taking the drug Ritalin to control hyeractivity.

Two child-behavior specialists testified that Matthews did not experience classic symptoms of psychosis and that Ritalin could not have triggered violent behavior. But a doctor said that Matthews' irrational conduct may have been exacerbated by the drug, which he had taken since the third grade. The jury deliberated for nearly 10 hours over two days.

Two friends of Matthews, Rob Peterson and Jonathan Cash, testified that Matthews told them in the fall of 1986 that he wanted to kill. They said two potential victims were rejected before Matthews decided on Ouillette because he thought Ouilette would not be missed.

Matthews took Peterson to see the body several hours after the Nov. 20, 1986, slaying. A few days later, Peterson and Cash went with Matthews to see the body after pep rally at Canton High School. Police found the body on Dec. 15, 1986, after receiving an anonymous letter from Cash.

Matthews told a psychiatric counselor later that he decided to kill someone after seeing the videotape "Faces of Death," which depicts animal and human deaths.