Upper West Side parents are being asked to pony up nearly $100 for classroom supplies like glue sticks, Crayons and washable markers — staples they could find by looking in the trash outside their kids’ schools.

Dunces at PS 166 threw away the very items they now want parents to buy, some of them new and still in their original packaging, according to recycling advocate Anna Sacks, who spotted the discarded items.

She also saw composition notebooks, copy and construction paper, folders, globes and even a child’s coat in the garbage.

Wasteful workers at a building that houses PS 333, the Manhattan School for Children, as well as two middle schools dumped colored pencils, chalk and oil pastels, paper, staples and erasers, she said.

“I think it’s really disappointing,” said Sacks, who posted what she found on Instagram account, @thetrashwalker.

“When it’s unopened, unused school supplies then it really just highlights that something is wrong. It’s kind of indefensible.”

PS 166 saw fit to chuck out hundreds of kids books, including “Little House on the Prairie” and “The Three Little Pigs,” Sacks said.

After spotting the supplies in late June, she moved some bags away from the curb to be collected and reused, then alerted the principal at PS 166, known as the Richard Rogers School of Arts & Technology because the famed composer was an alum.

But when Sacks returned to the West 89th Street school the next night, she discovered more supplies had been taken to the curb, some in a black garbage bag so no one could see what was inside, she said.

Sacks complained to Principal Debra Mastriano, who responded by e-mail, “We have donated books and materials to the Go Project as it is our goal to support literacy all around the city. And we will continue to do.”

Mastriano wrote in another e-mail that she would talk to her staff to make sure items weren’t discarded, adding they would “store all materials that could be donated at the main office.”

Sacks says she returned to the school a week later and yet again found supplies on the sidewalk, including books, markers, hand sanitizer and sticky notes.

The school brags on its Web site that it got a “perfect score” on its “zero waste school scorecard” in 2017-18, which the Department of Sanitation says recognizes compliance with garbage and recycling collection.

PS 333, on West 93rd Street, was given the top award for elementary schools in this year’s Zero Waste Schools Challenge, which rewards “outstanding programs in recycling, sustainability, gardening or cleanup,” according to the Sanitation Department.

“Schools should follow DOE policy and make every effort to find new homes for usable materials and equipment. This won’t happen again,” said Department of Education spokeswoman Danielle Filson.

The DOE said the discarded supplies outside the 93rd Street building did not belong to PS 333, but would not say which school tossed them.

Sacks, who last year found hundreds of books thrown away outside the private Columbia Grammar and Preparatory School, also on West 93rd, said it was upsetting to see such waste at public schools.

“There needs to be better systems in place so it’s really easy for the teachers to swap items or save items,” she said. “It can be something simple like putting a table outside the school and having it be a free table for the local community.”