No party for the poor.

PS 120 in Flushing held a carnival for its students Thursday, but kids whose parents did not pay $10 were forced to sit in the auditorium while their classmates had a blast.

Close to 900 kids went to the Queens schoolyard affair, with pre-K to fifth-grade classes taking turns, each spending 45 minutes outside. The kids enjoyed inflatable slides, a bouncing room and a twirly teacup ride. They devoured popcorn and flavored ices. DJs blasted party tunes.

But more than 100 disappointed kids were herded into the darkened auditorium to just sit or watch an old Disney movie while aides supervised — the music, shouts and laughter outside still audible.

The must-pay rule excluded some of the poorest kids at the elementary, where most parents are Chinese immigrant families crammed into apartments and “struggling to keep their heads above water,” staffers said.

“It’s breaking my heart that there are kids inside,” one teacher said.

The teacher hugged a 7-year-old girl who was “crying hysterically.”

“She was the only one from her class who couldn’t go, so she was very upset,” the teacher said.

The girl told others, “My mom doesn’t care about me.” But the teacher said parents possibly did not see or understand the flier that went home or didn’t have $10 to spare.

“Are we being punished?” one child asked an aide in the auditorium as kids sat there with no movie playing, a staffer said.

Principal Joan Monroe tacked up a list of the number of students per class: “How many attending, Paid,” and “How many not attending, Not paid.”

On Thursday morning, Monroe used the school loudspeaker to remind teachers to send in a list of kids who did not pay.

While teachers were handed a bag of little stuffed animals to give kids who paid for the carnival, one withheld them until she could add her own gifts for the half-dozen or so kids in her class who didn’t go.

“I think everybody should have gotten a prize, regardless,” she said. “They’re still part of our school community.”

The teacher hushed excited kids when they returned to class — some with bags of popcorn — after the carnival.

She had them put it away and do a quiet activity, so those who took part in the fun couldn’t talk about it and hurt those left out.

Another teacher was sickened by the inequity.

“If you are doing a carnival during school hours, it should be free,” she said. “It doesn’t matter if it’s one kid or 200 sitting in the auditorium. They all should have been out there.”

Frank Chow, president of the parents association that sponsored the carnival, said Monroe insisted that kids whose parents didn’t pay could not partake.

“She was saying it’s not fair to the parents who paid,” Chow said. “You can’t argue much, I guess. The school is under her.”

The carnival cost about $6,200, including fees to a carnival company, Send In the Clowns, and reaped a $2,000 to $3,000 profit, he added.

“I wish we just charged parents the cost, not to make extra,” Chow said.

The profit is earmarked for the pre-K, kindergarten and fifth-grade moving-up parties, he said.

PS 120 families also have paid annual PA dues of $15 per family. That money will be spent on window air-conditioning units, Chow said.

Monroe did not return calls and an email from The Post.