New London - Harbor School, the 100-year-old former elementary school on Montauk Avenue, likely will have to remain in use "for the foreseeable future" as the school district copes with rising student enrollment and limited space.

Among the reasons, school officials said, are a growing interest in the city's planned all-magnet school system and a breakdown in negotiations with the ISAAC Charter school to house three grades of students in the arts magnet pathway.

The district may have to consider altering the magnet pathway configuration or putting a non-magnet elementary school at Harbor - although the aim has been to become the state's first and only all-magnet school district.

On Monday, Chief Academic Officer Katherine Ericson presented the Board of Education with estimates of enrollment for the next school year and a report on future space issues.

For the 2015-16 school year, the district is projecting to enroll just shy of 3,500 students, up from about 3,430 this school year, according to Ericson. To receive a greater level of state funding, at least 25 percent of the students at the city's magnet schools must be from outside New London, and that contributes to the increase in enrollment.

"Our physical capacity is only 27 students more than what we're projecting we're going to have," board member Rob Funk said. "And that's not something we can change by just not accepting students from out of district, because if we don't accept students from out of district, we don't get the magnet funding."

Ericson also reported to the board on space issues that could arise at Winthrop Elementary Magnet School and at C.B. Jennings Elementary School, as it prepares to become a dual language magnet school in 2016.

In August, the district launched its new Early Childhood Center at Harbor School after the building sat vacant for a full year. Issues with transportation, last-minute school assignments and other issues created frustration among parents.

"We were ecstatic to get it open, but the time frame was not good for the district or families or the students," Ericson said. "So we're hoping to pre-empt that next year by having a pretty good estimate of where we're going to be."

Barring any major changes in the district's projections - which Ericson said intentionally err on the side of overestimation - the district "can make it one more year" without needing additional space, she said.

"We are very tight on space and we may need more space in the very near future," Funk said.

Once the school construction project recently approved by the City Council and voters is complete, in about five years, the district will have the capacity to enroll about 3,800 students, according to state-appointed Special Master Steven J. Adamowski.

"We will have enrollment issues and it will require careful planning, but it will work out in the end when the buildings are built," he said. "But we are going to have to have a thoughtful plan in between."

Compounding the space crunch is a stall in discussions with the Interdistrict School for Arts And Communication to have that downtown charter school act as the middle school piece of NLPS's arts magnet pathway. Adamowski said a partnership appears unlikely.

In addition to questions of whether ISAAC would have enough space, the school's charter stipulates an "integration mission" which sets ISAAC's enrollment at 50 percent New London students and 50 percent suburban students, Adamowski said.

"In order to accommodate all the rising fifth-graders, the school would have to become closer to 70 percent New London students and 30 percent suburban students, and they feel that would be a step backwards for them in terms of their charter," Adamowski said. "There may not be a partnership with ISAAC and, if that is the case, we have to plan for another set of contingencies."

Those contingency plans, Adamowski said, include the possibility of splitting the arts magnet pathway between Nathan Hale and Harbor schools, using Bennie Dover Jackson Middle School for both arts magnet and dual language students, or using Harbor School as a non-magnet elementary school.

"You are going to need to use Harbor School in one form or another for the foreseeable future in order to make this work and prevent any overcrowding in other schools," Adamowski said. "In virtually any option anyone can think of, Harbor needs to be in the mix."

The district has not yet researched any of its options in detail, and Adamowski said it is a topic the board will need to revisit after newly-appointed Superintendent Manuel J. Rivera has had about six months to immerse himself in the issue.

"This is something that needs to be the work of your new superintendent," Adamowski said, "to outline and refine some of these options, study it thoroughly and come up with the best alternative and the most financial viable alternative."

c.young@theday.com

Twitter: @ColinAYoung

Possible uses for the Harbor School building:

Option 1: Kindergarten through grade three of the arts magnet pathway, while Nathan Hale would house grades four through eight of the pathway

Option 2: Grades five through eight of the arts magnet pathways, while Nathan Hale would house kindergarten through grade 4 of the pathway

Option 3: A grade six through eight arts magnet pathway middle school, with Nathan Hale remaining as the K-5 arts magnet school

Option 4: A fourth, non-magnet elementary school