Class sizes in city schools jumped by the most in more than a decade this year - and youngest children are getting hit hardest.
The average elementary school class ballooned by about 4% to more than 23 students. Middle and high school classes grew by 1% to 2% to almost 27 students.
"It's a really sad story," said Leonie Haimson, executive director of Class Size Matters. "The kids with the highest educational needs tend to fall the furthest back. They benefit most from the individual attention."
After staying flat for the past six years, average kindergarten class sizes jumped to 21.7 from 20.7 students this year, preliminary data show.
Education Department officials blamed the increases on 5% budget cuts to schools, which translates to 1,650 fewer classroom teachers.
"We have managed to avoid massive increases in class size," said Marge Feinberg, a DOE spokeswoman.
Kindergartens experienced an enrollment increase of about 4,450 children compared with last year. The jump came at the same time the city closed kindergarten classrooms in its day care centers last year, pushing about 3,300 extra children into city schools.
The school with the largest kindergarten classes in the city is three blocks away from a day care center that was forced to shutter two kindergarten classrooms because of budget cuts. Public School 21 in Williamsbridge, the Bronx, now has an average of about 32 children per kindergarten class, compared with about 25 last year.
At PS 86 in the Bronx, kindergartens have been bursting at the seams for years.
"The teachers are great, but it is still overcrowded," parent Margaret Hamilton said.
A third of all the overcrowded kindergartens are in Brooklyn.
"It's gross mismanagement," said United Federation of Teachers President Michael Mulgrew.
"It's common sense. When you close some kindergartens, then other kindergartens are going to get more kids.