New York City will add 4,268 seats to city schools' full-day prekindergarten classrooms by September, the mayor's office announced Wednesday.

It's the first major expansion of the city's nascent, universal pre-K program. Funded by the state, the $300 million-a-year initiative is set to serve each of the city's 73,000 eligible students by the 2015-2016 school year. There are currently about 16,000 seats for full-day, pre-K programs in public schools. This year's additions will span 140 schools in all five boroughs.

"We have been planning every facet of these programs to ensure we were ready to launch the moment funding was secured," Mayor Bill de Blasio said in a statement. "Today, the rubber hits the road, and families will have more options for their children."