Lax discipline at a top city middle school enabled the sexual abuse of a teen girl last month, her irate parents told The Post on Thursday.

The father of an eighth-grader at Marie Curie Middle School in Bayside said a classmate sexually harassed her beginning in September — relentlessly asking her to have sex and questioning her bra size.

He pulled his pants down in a classroom in October and told a classmate to get the girl to join him, her father said.

“But no one from the school ever told us about it,” he fumed. “They gave him detention and just put him back in the class the next day and it got worse from there.”

The torment escalated on Nov. 26 when the boy again demanded sex from the teen, groped her leg and groin and then grabbed her from behind, classmates told a teacher.

Her parents were called but the father contacted cops after administrators dithered on a punishment.

The 13-year-old boy was arrested and charged with misdemeanor forcible touching.

“He asks me disgusting questions like what my bra size is and if I want to ‘smash,’” the victim wrote in a statement to investigators. “I feel like whatever I say doesn’t matter.”

Several classmates backed up her accounts in separate statements.

“This has been bothering [the girl] for a long time and I don’t want her to be scared to go to school for the actions of one student,” one wrote.

The girl’s father said she was too ashamed and embarrassed to tell her parents about the abuse but finally broke down to a doctor after last month’s incident.

“She just said she was so scared,” her mother said. “This really has a big impact on a young child. And these schools don’t do anything.”

A sympathetic teacher told her parents about the prior bullying incident in October and the family has since retained an attorney.

A former staffer at the highly regarded school said that teacher morale has cratered in recent years because discipline is no longer applied.

“It’s at an all-time low,” he said. “It’s no secret. If this is what’s going on at a good school in Bayside, you have to wonder what’s going on everywhere else. The kids know they can get away with anything.”

DOE spokeswoman Mirand Barbot said: “Students deserve safe and supportive environments, and schools must report all incidents and notify parents. We are looking into this further and will take any action necessary.”