For the first time since at least 1970, Chicago Public Schools will serve fewer than 400,000 students.

District spokesman Bill McCaffrey confirmed that there are at least 3,000 fewer students in the public school system. The decline keeps Chicago just ahead of Miami-Dade County Public Schools, which enrolls roughly 380,000 students, including pre-K students, vocational students and those in charter schools.

CPS took its official head count on Monday, the 20th day of school. The past two years, the district has counted on the 10th day as well, in order to adjust school budgets to account for the difference between enrollment projections and how many students actually show up. For the second year in a row, schools that didn’t meet their enrollment targets were held harmless and got to keep the money budgeted to them over the summer.

Enrollment in CPS had been steadily declining for the last decade, but remained relatively flat from 2008 to 2012. In the last two years, since CPS closed 50 district-run schools, the system lost about 6,000 students.

At the same time the district’s been losing students, CPS has opened more than 140 new schools, most of them privately run charter schools. Officials did close schools at the same time, but the openings outpaced the closings.

Enrollment over time in Chicago Public Schools

*Does not include Pre-K, charter and contract schools or alternative schools.

**Preliminary estimate based on confirmed decline of at least 3,000 students.

Wendy Katten, executive director of the city-wide parent group Raise Your Hand, said the decline is really sad, but not that surprising.

“We hear a lot from parents about the instability of the policies of the district,” Katten said “The constant school actions, the opening and closing of schools, and the budget cuts. I think a lot of parents are looking for more stability in their children’s schooling.”

Michael Casserly, the executive director of the Council of Great City Schools, said enrollment in urban districts can take a hit when there’s a lot of turmoil. In CPS’s case, that included the first teachers’ strike in 25 years and the mass closure of 50 public schools.

“But in situations like that you’ll often find that enrollment bounces back,” Casserly told WBEZ. He said the council recently surveyed public school parents in urban districts and found that more than 80 percent are satisfied with the schools.

Casserly also noted that declines are directly related to population declines. Indeed, Chicago has lost school-aged children in the last few decades. But the percentage of those children being educated by CPS has increased.

Census Figures vs. CPS Enrollment

Source: U.S. Census Bureau, Chicago Public Schools, Illinois State Board of Education, Chicago Tribune (for the 1970 number of CPS students).

In the district’s 10-year Master Facilities Plan, CPS commissioned Educational Demographics and Planning, Inc. to calculate enrollment projections for the next ten years. The plan estimates a 1 percent increase in the number of school-aged children in Chicago.

CPS’s McCaffrey said until the preliminary 20th day enrollment numbers are vetted, the district is unable to speculate why the schools lost children. More detailed numbers will be out in the coming days and that will help CPS understand what areas of the city are losing the most kids and what grade levels see the biggest drops.

Andrew Broy, executive director of the Illinois Network of Charter Schools, said he expects an increase in the number of children in charter schools. CPS opened four new charter schools this year and is adding grades at a number of existing campuses.

Broy did admit that some charter schools are struggling to fill open seats.

“We’re seeing more places, on the West Side and parts of the South Side, where charter school enrollment numbers haven’t kept up with the campuses being added,” Broy said Monday, noting that one-third of all charter schools currently have room for more students.

But Broy said charters are also the reason many families have chosen to stay in the city.

“I would argue that if we did not have charter schools over the past 10 years we would see a much higher out-migration pattern in Chicago,” he said.

CPS needs to confront the fact that its enrollment is declining, Broy said, but he also said the district needs to continue adding high-quality options for parents.

Katten, with the parent group Raise Your Hand, said CPS officials should stop opening new schools and focus on ones they have.

“There should probably be a moratorium on opening new schools of any kind,” she said. “Parents want a commitment, whether they’re in charter schools or district schools, that those existing schools are getting attention.”

Linda Lutton contributed to this story.

Becky Vevea is a producer and reporter for WBEZ. Follow her @WBEZeducation.