Big Apple parents are getting a crash course in cutthroat capitalism at their kid’s schools, which are strong-arming them into buying supplies at sky-high prices to pad the bottom line.

The money-making scheme is generating windfall profits — tens of thousands of dollars citywide that’s getting tucked away in school slush funds, The Post has found.

At least 10 NYC schools’s have worked out a private deal with a small Chicago-based business, Yubbler, to sell supplies to parents — and split the profits with the PTA or school.

The company offers packages of schoolhouse basics — notebooks, crayons, paper and more — at inflated prices, in some cases up to double what stores and online retailers charge, The Post found.

But excess supplies are apparently hoarded in closets and storerooms, creating an artificial shortage.

Two Upper West Side schools — PS 333 Manhattan School for Children and PS 166 The Richard Rodgers School of Arts & Technology — amassed so many staples that bagfuls of new or unused books and crayons were found in the trash recently outside both schools.

One mom of a former PS 333 student said she stumbled across a storage room in the school basement that was jam-packed with parent-purchased supplies.

“When I walked in, I said ‘Whoa! What’s all this stuff?’” recalled Ingrid Flinn.

An ex-worker at the school described closets on the fourth and fifth floors, including one so stocked with donated paper towels, disinfectant wipes, and Ziploc bags, “It looked like a grocery store.”

Another closet was bursting with pencils, crayons, notebooks and other classroom staples, the former employee said.

“They had a ton of stuff — a lot more than they needed,” she said. “But they keep asking parents to buy the same things every year.”

With the Department of Education’s $24 billion annual budget, some parents wonder why schools ask them to buy pencils.

Insiders suspect the real purpose behind pushing parents to buy supplies is for the schools to avoid spending money they get from the DOE on supplies. Their share of the profits can be spent on anything, including music or art programs, field trips, and other extras.

The arrangement gives an edge to schools with more affluent parents, who typically consider Yubbler and similar services a convenience and also give big bucks to PTA fundraisers.

That flies in the face of Chancellor Richard Carranza’s call for “equity” among public schools.

It’s unclear how Yubbler determines its profits.

Owner Pablo Yugaz, said he and co-founder Luis Yugaz, his brother, employ four full-time staffers and 10 part-timers, some in South America.

After four years in business, he and his brother, who hold other full-time jobs, collected payments from Yubbler for the first time last year, he said.

Yubbler buys all its supplies wholesale from Office Depot, and marks up the prices for schools, said Yugaz.

“We try to be at their retail prices or lower,” he said.

But the Post found some Yubbler items selling for less even at OfficeDepot.com.

Yubbler charges $9.49 for a box of 12 Ticonderoga pencils, while the same box goes for $2.19 at Target.com and $1 on sale from Office Depot online.

Yubbler charges $87.69 for each Westcott caddy with 25 blunt scissors, while the same item costs $50 at Target.com.

Yubbler charges $56.99 for 10 reams of Office Depot copy paper, while Staples sells the same quantity of Hammerhill copy paper for $32.99.

One PS 333 employee blasted the arrangement as “kickbacks for crayons.”

“They’re ripping parents off,” said the staffer who asked not to be identified for fear of retaliation.

“Their prices are really inflated when compared with other retailers that carry the exact same products.”

Over the summer, PS 333 emailed parents 11 reminders to buy from Yubbler, touting the “discounted prices” and extra funds for the school.

“We continue to offer a program that will help the school and make it a breeze for parents to get school supplies for next year,” it reads.

“Yubbler.com is making our supply lists available for online purchase at discounted prices. The best part is that Yubbler will donate 50 percent of the profits back to the school.”

It adds as a footnote: “You do not have to purchase through Yubbler. You can purchase your supplies anywhere! West Side Stationery is a great resource for supplies, as are your local shops.”

Families were asked to pay $76 or $83 for each kid in grade K to 5 for packages that include both individual supplies, like a box of crayons, and “mass quantities” of items such as copy paper, plastic bags, and glue sticks.

Yugaz would not give The Post a written accounting, but said PS 333 families shelled out $38,000 for supplies last year.

In turn, he said, Yubbler sent the school’s parents association a check for $4,300 — about 11 percent of the revenues.

On its website, Yubbler touts endorsements by PS 333’s former PA co-president Brad Rothschild, citing $5,939 in funds raised.

It also names PS 166’s former PTA president, Erin Volkmar, citing $5,015 raised; and a “supplies coordinator” at JHS 54 Booker T. Washington Middle School, citing $6,995 raised.

PS 133’s current PA co-presidents, Diane Shoemaker and Jason Isbell, said only, “The arrangement with Yubbler is with the school and not the Parents Association.”

It’s a well-endowed PA. Its non-profit, Friends of MSC, raised $363,892 in FY 2016-17, according to its latest tax filing.

Principal Claire Lowenstein did not respond to an email with questions.

“It’s kind of terrifying how this operation works — how the prices are jacked up and the incentive for principals to throw out perfectly usable items on the street,” the PS 333 staffer complained. “What’s worse, nobody has been able to give a straight answer as to what this money has been spent on, and it’s been at least several thousand dollars a year for the last five years.”

Bagfuls of new or unused school supplies were recently tossed to the curb outside PS 333 and PS 166, which also uses Yubbler.

Recycling advocate Anna Sacks rescued brand-new notebooks, copy and construction paper, folders, and globes in the PS 166 garbage. At PS 333, she found colored pencils, chalk and oil pastels, paper, staples and erasers, The Post reported.

“It seems like P.S. 333 has a dire shortage of these same school supplies,” the staffer said of the sales pitch to parents.

Yubbler is one of other such vendors who pitch the same service.

Queens-based Star Student Supply, has deals with about 35 schools in the city, said president Nathan Greenfield.

Based on teacher requests, his company buys supplies wholesale from manufacturers, marks up the prices and sells packages to parents ranging in price from $20 to $100 or more, he said.

The schools’ PTAs or Parents Associations can further mark up the packages — tacking on $5, $10, or whatever they want to collect from each sale.

DOE spokeswoman Danielle Filson said it does not sanction companies such as Yubbler: “Families are not required to purchase school supplies from any particular vendor, and schools will also ensure that every student has the necessary supplies regardless of their ability to pay,” she said.

The DOE’s Teacher’s Choice program also gives teacher up to $250 each to spend on supplies.