Leonie Haimson of Class Size Matters has released a report on the unintended consequences of Mayor De Blasio’s rapid expansion of Pre-K, his proudest achievement in education. The plan was rushed ahead with little forethought.

Her report begins:

School overcrowding in NYC has been worsened by the expansion of pre-K and 3-K classes, as detailed in a new report, “The Impact of PreK on School Overcrowding: Lack of Planning, Lack of Space.”

About 575,000 students, more than half of all students, attended schools that were at or above 100 percent capacity in 2016-2017, according to data from the NYC Department of Education. In recent years, overcrowding has worsened significantly, especially at the elementary school level. Nearly 60 percent of elementary schools are at 100 percent or more and 67 percent of elementary grade students attend these schools. This is due in part to the fact that enrollment in these grades has increased faster than new school construction.

The report’s analysis finds that 14,220, or more than half of the pre-K students enrolled in public elementary schools in 2016-2017, were placed in 352 schools that were at 100% utilization or more, thus contributing to worse overcrowding at these schools for about 236,000 students.

In about one quarter (22 percent) of these schools, the expansion of pre-K actually pushed the school to 100 percent or more. As of 2016-2017, 76 elementary schools, with a total of 45,124 students, became overutilized, according to the DOE’s data, because of the additional number of pre-K students at their schools.

In addition, thirty schools with pre-K classes had waitlists for Kindergarten, necessitating that these children to be sent to schools outside their zone and sometimes far from home.

District 20 in southwestern Brooklyn is the most overcrowded district in New York City with a critical shortage of elementary school seats.

The average utilization of elementary schools is 130 percent. Yet the DOE continued to place pre-K classes in already overcrowded District 20 schools, despite the presence of an under-enrolled pre-K center nearby.

Laurie Windsor, the former President of the Community Education Council in District 20 said: “It is appalling how the DOE insists on keeping pre-K classes in elementary schools when there is such severe overcrowding and families are forced to travel for Kindergarten, sometimes quite far away, without available public transportation. Especially egregious is that there are pre-K centers nearby which could absorb these classes easily. This practice has put unnecessary hardships on families and is insensitive to the needs of the community.”