Six years after a sixth-grader choked to death while stuffing her mouth with marshmallows as part of a classroom game, a lawsuit blaming her suburban school district went to trial Thursday.

Francis Patrick Murphy, a lawyer for the girl's family, argued that a lack of supervision led to the death of 12-year-old Catherine "Casey" Fish (search). But an attorney for the Glenview School District contended the youngsters were never out of the teachers' sight.

The lawsuit seeks unspecified damages.

Murphy told the jury that the teacher had walked out of the room to talk to a janitor when Casey and her friends started playing "chubby bunny" — a race to stuff as many marshmallows in their mouths as they could and still say the words "chubby bunny" three times.

Casey choked on four marshmallows and collapsed. She died at a hospital a few hours later.

"You have to make sure that when children are doing something that might be dangerous you are there to protect them," Murphy told the jury in opening statements. "Effective supervision timely acted upon would have saved Casey. Casey's parents would be sitting at her high school graduation next week."

Thomas DiCianni, an attorney for the school system, said the children were in a room in the middle of a group of open classrooms with sliding doors and a low wall between the rooms and the hall. Two teachers had a view into that room, so at no time were the children unsupervised, he said.

DiCianni also raised questions about the medical examiner's ruling that Casey choked to death, saying unknown health problems could have been involved and were missed in the autopsy.