More than 900 classrooms for the city’s youngest students are contaminated with peeling lead paint that can cause devastating and permanent brain damage, according to new data from the Department of Education.

Recent inspections found hazardous, deteriorated lead paint in 302 of 797 schools that serve kids under age 6 and were built before 1985 — or more than one-third of the total, statistics show. The worst findings were in two schools — PS 108 in Brooklyn and PS 49 in The Bronx — that each have 12 potentially dangerous classrooms.

“This is awful,” said Leonie Haimson, founder of the parent advocacy group Class Size Matters. “Even children with tiny amounts of detectable lead in their blood are more likely to have academic and behavior problems.”

It was unclear how many kids may have been exposed to lead in the 938 classrooms before the testing, which was conducted in late June after the school year ended.

A spokeswoman said the DOE planned to send e-mails and letters to principals and parents whose kids were potentially affected.

The testing followed a WNYC/Gothamist investigation that found lead contamination from paint in four schools, including dust with lead levels more than 100 times greater than city safety standards.

The DOE quietly posted a massive spreadsheet with results of the testing on its Web site on Wednesday night, burying the data on a page that’s two clicks away from its “About Us” tab on the home page.

The data says none of the classrooms had yet undergone “stabilization” to seal the peeling paint with primer and cover it with lead-free paint. The DOE claims all that work will be done in time for the first day of school on Sept. 5.

Brooklyn mom Shanna Jordan, 30, said one of her kids — a boy waiting to enter first grade — attended pre-K and kindergarten at PS 108 and was diagnosed with lead poisoning last year after he fell behind academically and became hyperactive. Jordan said her home tested negative for lead paint but she “didn’t bother to check the school.”

“I would think they would be up on it, to check the schools,” she fumed. “They’re supposed to make sure the kids are safe.”

A spokeswoman for Mayor de Blasio downplayed the risk posed by lead paint in classrooms, saying the city Department of Health has found that “schools haven’t shown to be a main source of lead exposure in kids.”

DOE spokeswoman Miranda Barbot also insisted, “Our schools are safe, and this summer we’ve enhanced our protocols and strengthened communication with families around the steps we take to prevent lead exposure for kids under 6.”

She added the DOE would “remain vigilant throughout the year and regularly inspect, test and immediately address any concern.”