CAMBRIDGE, Mass. — A Harvard University graduate student was convicted of manslaughter and sentenced to six to eight years in prison yesterday for stabbing a teenage father to death with a knife he said he used in self-defense during a fight.

Prosecutors had sought a first-degree murder conviction for Alexander Pring-Wilson, arguing he became enraged when Michael Colono ridiculed him for being drunk. The defense argued that Colono and his cousin were brutally beating Pring-Wilson when he lashed out with a knife and inflicted the deadly wounds.

Judge Regina Quinlan could have given a sentence ranging from probation to 20 years in prison.

Pring-Wilson’s mother, Cynthia Pring, said she understood the Colono family’s pain. “I feel for them so strongly,” she said. “My son feels for them so strongly.”

The case represented a collision of two worlds. Pring-Wilson, the privileged son of Colorado lawyers, was studying at Harvard for his master’s degree in Russian and Eurasian studies and planning to attend law school. Colono, an 18-year-old high school dropout, had earned his GED and was working as a cook at a Boston hotel. He died the day before his daughter’s third birthday.

Defense lawyer Ann Kaufman, in tears as she asked the judge to sentence Pring-Wilson to probation, said her client had been unfairly portrayed as a product of an elite upbringing.

“He’s worked all of his life. He comes from a family where all the children in the family worked,” said Kaufman. “This isn’t about race, or class or privilege or wealth. … What it’s about is what happened on that street between three people.”

On April 12, 2003, Pring-Wilson was walking home after a night out with friends. Colono, his cousin and his cousin’s girlfriend were waiting for a pizza outside a restaurant.

“Michael Colono made fun of the defendant and it cost him his life,” Assistant District Attorney Adrienne Lynch said.

Pring-Wilson testified he was defending himself. In the courtroom, he re-enacted the fight, dropping to one knee to show how he bent beneath a succession of blows.

“I was thinking, what’s going to stop these guys? … Are these guys going to know to stop when I’m dead?” he testified.

Prosecutors pursued a first-degree murder charge against Pring-Wilson. One of those conditions must be met to convict for first-degree murder, which carries a mandatory sentence of life in prison without parole.