It’s back to school shopping season — and families aren’t the only ones ponying up for school supplies.

According to AdoptAClassroom.org, a crowdfunding website for educators, teachers in K-12 classrooms spend on average $600 of their own money each year on goods for their students.

Allison DeGrazia saw other teachers using AdoptAClassroom.org when she started as a fifth-grade teacher at P.S. 34 in the East Village six years ago, and she has been using it ever since to help offset what she spends.

With donations raised through multiple crowdfunding sites, including AdoptAClassroom.org and DonorsChoose.org, DeGrazia has bought basic supplies, like pencils and crayons, often having her students vote on what to buy for the classroom.

“It becomes more meaningful — those pencils they might break or throw on the floor are the pencils the donors got us, so we need to take care of them,” she said. “It gives them ownership.”

DeGrazia has also been able to buy several tablets, which are used for math and reading programs like IXL and Raz-Kids.

“It’s a nice mix of being able to use it for the things that we need, and to be able to provide them with things other schools have that they don’t and make the classroom more equitable,” she said.

DeGrazia is not alone; according to AdoptAClassroom.org, there are more than 850 New York City teachers in grades K-12 at public, private and charter schools actively crowdfunding on the site — up from fewer than 500 a decade ago. NYC has the second-highest number of teachers registered on AdoptAClassroom.org, which launched in 1998, among cities nationally.

“It’s obviously a real high-need area,” said Ann Ness, executive director of AdoptAClassroom.org, noting that teachers are increasingly buying personal items for students in addition to school supplies. “We hear every day from teachers who are buying coats, socks or shoes for their students in a way that simply wasn’t done 20 years ago.”

To help one school in need, the organization recently teamed up with Burlington Coat Factory to donate $10,000 to Renaissance School of the Arts, a middle school in East Harlem, where 83 percent of students come from low-income households. The funds will be spread out equally to all teachers to help stock their classrooms for this school year.

Dance teacher Danielle Winsko is already thinking about what to buy for her classroom — from books pertaining to dance to stability balls so she can do more intensive conditioning with her students.

Winsko, who is entering her seventh year teaching at the school, estimates she spends more than $1,000 a year on her classroom — from notebooks and pens to cleaning supplies for her studio to leotards to Broadway tickets for shows such as “Cats” and “The Lion King.”

“It was done for me — I’ve gone to public schools my whole life,” said Winsko, who studied dance at Frank Sinatra School of the Arts in Long Island City. “If I didn’t have those opportunities when I was young, I wouldn’t have gone into the arts. It’s giving back.”