Six weeks after assuring the public that it had lead paint problems under control, the City of New York has released data showing lead poisoning hazards in more than 900 classrooms used by children under 6.

The data followed a Gothamist/WNYC investigation this spring that found elevated levels of lead in four grade school buildings. At first, the mayor’s office responded that schools “do not present a principal risk of lead exposure” and said that the education department had a robust system to monitor and remediate deteriorating lead paint.

However, after New York’s congressional delegation demanded the Department of Education step up its protocols for testing lead, city officials promised to intensify lead screening of classrooms before public school students return this fall.

The results of the latest inspections, limited to classrooms used by kindergarteners, pre-kindergarteners and 3-year-olds, show that roughly one out of every five classrooms inspected had deteriorated, peeling, or chipped paint. The DOE first gave the data to the education website Chalkbeat and confirmed it Thursday to Gothamist/WNYC.

Listen to Christopher Werth discuss the findings on WNYC:

The education department, which has posted the results online, continued to insist Thursday that public schools are safe.

The department says it will immediately remediate paint in 938 classrooms where lead-based paint is present and there is visible deterioration. It’s also created an online tool for parents to report deteriorated paint conditions in schools. In addition, inspectors found that another 1,307 classrooms had visibly deteriorating paint that was not lead-based.

The education department also said it will begin inspecting first-grade classrooms after WNYC’s reporting revealed it was not in compliance with the city’s health code, which requires visual inspections for all classrooms occupied by children under six years of age.

Scientific research shows that exposure to lead, even at low levels, can cause learning disabilities, hyperactivity, and other behavioral problems. Young children are particularly susceptible because their brains are still developing and they are more likely to get small pieces of paint on their fingers and put their fingers in their mouths.