A scathing report claims city schools are vastly overcrowded because the Department of Education has added tens of thousands of seats without the proper space to accommodate them.

The Campaign for Fiscal Equity, a group behind a successful lawsuit to direct more state aid to city schools, along with elected officials and United Federation of Teachers president Michael Mulgrew, said the city has added 130,000 seats for students over the past 12 years, but department data provided to the group show an increase of space for only 80,000 seats.

A department spokesman called the study “deeply flawed.”