CAMBRIDGE, Mass. (AP) _ A jury began deliberations Tuesday to decide whether a teacher is guilty of raping a 15-year-old student or the boy fabricated the tale.

Karen Cross, 33, is accused of luring the boy to her home on Valentine's Day 1990 and seducing him. Prosecutors say they had sex three times in six weeks.

In closing arguments Tuesday in Middlesex Superior Court, a prosecutor told the jury Cross relentlessly pursued the student in a quest to ''enter his little world.''

''He was probably flattered by her interest in him in a sexual way,'' said Assistant District Attorney Sheila Calkins, adding that the boy allegedly ended the affair.

''Who was the adult here?'' Calkins said. ''Who ended it? He did.''

Cross claims she is innocent and that she only tried to help the student she described as disturbed. The defense claims he invented the story.

She is charged with three counts of rape of a child and could receive a maximum sentence of life in prison if convicted. There are no allegations of physical force, but the 15-year-old was not legally old enough to consent to sex.

Defense attorney James Dangora questioned the boy's credibility, saying he changed his story several times while testifying last week.

The boy, now 16, was then a sophomore at Tyngsboro Junior-Senior High School, in Tyngsboro, about 20 miles north of Boston. He was in a special class because of learning difficulties.

Cross, who is on leave from her job, admitted on the stand that she had the boy to her home and exchanged several gifts with him in 1990. But she said such visits from students were common.

''I had students over all the time,'' Cross said. ''I was helping a student in need.''

Eight witnesses testified in the trial, which began Thursday and included exhibits of love letters Cross allegedly wrote.

Two lines in the letters read: ''God, I wish I didn't care about you so much,'' and ''I can't get you off my ... mind.''