In 2013, the year before New York City Mayor Bill de Blasio took office, there were about 20,000 free, full-day pre-K seats available to children. Three years later, the city’s preschool landscape looks vastly different. For the 2016-2017 school year, the city had free, full-day seats for more than 70,000 students. Now New York is trying to share what it has learned from this expansion with cities across the country. On Thursday, New York will host a daylong learning lab with leaders from 12 other cities, including Boston, Philadelphia, Chicago and Seattle. During the event, early learning leaders plan to discuss topics like family outreach and sustainable quality programming, and share insights and challenges from their own cities’ initiatives.