A Harvard University graduate student was convicted of manslaughter and sentenced to six to eight years in prison Thursday for stabbing a teenage father to death with a knife he said he used to defend himself in a fight.

Prosecutors had sought to convict Alexander Pring-Wilson, 26, of first-degree murder, arguing that he became enraged when Michael Colono ridiculed him for being drunk. The defense argued that Colono and his cousin were beating Pring-Wilson when he lashed out with a knife in April 2003.

The case represented a collision of two worlds. Pring-Wilson, the 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, 18, a high school dropout, had earned his high school equivalency degree and was working as a cook at a Boston hotel. He died the day before his daughter turned 3.

Defense lawyer Ann Kaufman, pleading with Judge Regina Quinlan to sentence Pring-Wilson to probation, said her client had been unfairly portrayed as a product of an elite upbringing.

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