The city’s budget plan will not solve the problem of school overcrowding, a new report argues, despite the mayor’s pledge to devote new resources toward reducing the number of students who attend class in jam-packed buildings.

More than half of elementary schools are now more crowded than their space plans allow, and average class sizes have increased over the past five years, according to the 62-page report by the advocacy group Class Size Matters. The addition of thousands of new pre-kindergarten seats and a new state law that forces the city to find space for charter schools will only make the situation worse, the report says.

As the city’s population swells, there will be a need for more than 100,000 additional classroom seats, the report estimates. Meanwhile, the city’s latest five-year school construction plans calls for less than 40,000 new seats.

“If this plan is adopted, students are likely to be crammed into even more overcrowded schools and classrooms five years from now,”  Leonie Haimson, Class Size Matters’ executive director, said in a statement.

The report also objects to the way the city calculates how much space is available in school buildings, and criticizes its plan to get rid of classroom trailers without creating a matching amount of space inside school buildings.

Department of Education officials pointed out that the mayor’s capital plan sets aside funds to add more school space, reduce class sizes, and remove some of the trailers.

“We are tackling the serious issue of overcrowding head on, which is why we have proposed $4.4 billion dollars to open nearly 40,000 new seats, many in historically overcrowded districts, in addition to creating a school space working group that is engaging across City agencies and with community leaders to recommend long-term solutions and alleviate the problem,” said department spokesman Harry Hartfield.

You can read the full report here.