An empty classroom at a Queens elementary school. View Full Caption DNAinfo/Ewa Kern-Jedrychowska

BRONX — More than half of the city’s 1.1 million public school students attend overcrowded schools, according to a new report from the watchdog group Class Size Matters.

Despite the Department of Education’s addition of more seats and new buildings, many families feel the situation is getting worse as existing seats are being chipped away due to lost leases, schools being co-located together, or the elimination of annexes, mini-buildings and trailers housing temporary classrooms, according to the report released Thursday.

As trailers housing temporary classrooms — with nearly 8,000 seats — are expected to be phased out entirely, it may further strain school buildings, the report warns.

Roughly 575,000 students attended schools in 2015-2016 that were at or above 100 percent capacity, the report said, citing Department of Education enrollment data.

“School overcrowding has a severely negative impact on the quality of education,” the report stated, “including students forced to eat lunch too early in the morning or too late in the afternoon, a lack of dedicated space for art or music, too little time each week to exercise or play sports in the gym and, most importantly, excessively large classes.”

Last fall, roughly 330,000 students across the city were sitting in classes of 30 kids or more, the report says.

A recently lapsed lease for an annex at Riverdale’s popular P.S. 24, for instance, forced the school to convert a small planetarium into new classrooms.

The school — which saw its enrollment jump from roughly 720 in 2007 to 1,075 last year — had already lost its dedicated computer and music rooms, and its library was converted into a “media room” with computers but few books.

With the annex closed — to make way for a private pre-K center — P.S. 24’s already overcrowded building had to squeeze 200 more kids inside.

“The last seat that was added to the Riverdale community was 1970,” Robert Heisler, P.S. 24 parent association co-president, said in the report. “That’s 46 years ago, and some of those seats ... were a part of the annex which is now closed. So we are going backwards.”

The overcrowding situation had become heated at the Riverdale school, with allegations that an elected official was racially profiling students during the admissions process.

Additional overcrowding concerns loom on the horizon.

Enrollment is expected to increase over the next five to 10 years in these districts, like District 15, which includes Carroll Gardens, Red Hook, Park Slope and Sunset Park; District 24, which includes Corona, Elmhurst, Ridgewood, Long Island City; as well as Queens high schools.

In District 24, one of the city's most overcrowded districts, elementary schools average 125 percent capacity. The DOE's February 2017 capital plan estimates the district needs about 9,400 seats, but only about half of those seats funded, the report said.

And while the DOE plans to remove 623 temporary seats, according to the report, a district spokesman said those seats are already included as part of the 9,400 shortfall as the temporary fix wasn't ever counted as a permanent solution.

DOE officials defended their record, noting that 10 new schools and building extensions opened this year with 6,000 seats across the city, including 1,100 of which were in District 24.

“We are dedicated to addressing overcrowding and are making substantial investments to reduce class sizes over the next several years, including dedicating $4.5 billion to create more than 44,000 seats in overcrowded areas across the city," DOE spokesman Michael Aciman said.

Across the system last year, the overall average class size was 26.2 students per class, representing a 0.2 decrease from the year before, according to DOE data.

In kindergarten through third grade, the average class size was 24.2 students per class, down 0.4 from the year before.

"Last year, class sizes decreased in grades K-12 and we will continue working closely with [Community Education Councils], families, community members and elected officials to identify suitable locations for new schools across the city," Aciman added.