When the boxes started arriving — stuffed with markers and paper, stickers, novels, and a butterfly garden — it felt like Christmas morning to teacher Valerie Hart.

Like millions of educators across the country, Hart typically spends hundreds of dollars every summer on supplies to make her classroom warm and inviting for her students at St. Eugene School in Upper Darby. But this year, the things she needs came through a social media campaign dreamed up by a Texas teacher.

“It’s amazing how a simple idea was able to transform so many teachers’ lives,” said Hart, a second-grade teacher. “I cannot wait to start school and explain to my students how we received these items from many generous people, some friends and family of mine, but others complete strangers.”

The boxes in Hart’s Delaware County classroom appeared in a way because of Courtney Jones, who spent $1,000 on classroom supplies in her first year teaching fourth grade in Texas, and who has shelled out hundreds every year since then.

Jones knows she’s not different from the vast majority of educators. According to the federal government, 94 percent of U.S. teachers pay for classroom supplies for which they aren’t reimbursed.

“Parents are frustrated, districts are frustrated, and teachers are frustrated, but we’re the ones bridging that gap, and something’s got to give,” said Jones, who teaches in a poor, rural district.

Enter #clearthelists, which Jones, a third-year teacher, started in July with a closed Facebook group asking teachers to post classroom wish lists. Three weeks in, 30,000 educators from around the country had joined, buying each other supplies from lists as a way to support their peers. To participate, teachers create lists on Amazon or post project pages on Donors Choose, then publicize their lists on Twitter, Facebook, or Instagram; once the projects are funded, the supplies get shipped directly to the educators.

Her campaign went viral, trending nationally and drawing thousands of donors from beyond the teacher ranks. Jones appeared on Today. Celebrities fulfilled teachers’ wish lists and spread the word about #clearthelists.

Jones now estimates that 400,000 people have participated in the movement; #clearthelists hashtags are in every state, with projects from modest to grand.

“I’m not surprised this took off, because it is such a widespread issue, but I’m shocked by the impact,” said Jones, who teaches in a district that reimburses teachers $80 a year for classroom supplies, $20 less annually than Philadelphia School District teachers’ allotment.

School supply reimbursement amounts vary from district to district, and some teachers get annual school-supply donations or stipends from parent organizations. But teachers agree: Even in well-funded districts, they’re reaching into their own pockets, often spending well over their district allocation before students even report to class.

Ashante Carr, a third-grade teacher at Waring Elementary in Philadelphia’s Spring Garden section, can hardly believe her luck: Strangers bought her students lap desks, clipboards, and sturdy, tall stools for reading.

In the past, Carr hasn’t gone the way many teachers now do, listing projects on Donors Choose and other crowdfunding sites. Instead, she spent from $500 to $1,000 a year out of her pocket on supplies, decor, and materials to make her classroom bright and homey. And because she has taught at multiple grade levels, she’s had to start over more than once.

She’s not rich, but it’s tough to say no when her students have needs, Carr said.

“I try to hit the sales in the summer, and it’s been helpful that Target does a teacher discount,” said Carr. “I work summer school and use part of the money I make to buy a class set of all the books I can.”

Now that Carr’s original list was funded, she’s added a few things, but is mostly spending her time helping other teachers draw attention to their lists and purchasing items for others when she can.

Edwin Minguela, a third-grade teacher at John Marshall Elementary in Frankford, has put his wish list out — tissues, hand sanitizer, pencils, markers, glue sticks — but hasn’t had any takers. He’s still plugging away, though.

Going into his third year of teaching, Minguela estimates he’s spent $6,000 on materials for his students. He’s had some luck with Donors Choose projects, but his pupils’ needs are vast.

“Not every kid brings supplies,” said Minguela. “I have some kids that don’t even bring a backpack.”

The movement is by no means eliminating teachers’ need to self-fund their classrooms, said Jones, the founder. But it can take some of the burden off them, and the buzz from having a stranger send your students boxes of books or sports equipment or art supplies is hard to explain, she said.

“It’s just been absolutely incredible to see how life-changing it is,” said Jones.