A bar graph illustrating enrollment at Preston's elementary and middle schools over the past 45 years resembles the first deep dive in a roller coaster ride followed by a gentle incline, another drop and a hint at a new rise to come.

In 1970, Preston schools enrolled 841 students in grades kindergarten through eight. Fifteen years later, the number was nearly cut in half to 462, then it climbed to 522 by 2003 and down again to 439 in 2015 – although boosted by the move to add universal preschool at Preston Veterans' Memorial School.

The numbers and detailed analysis of enrollment projections are the centerpiece of a 17-page report commissioned by school officials from Peter M. Prowda of Simsbury. Prowda based his projections on a combination of recent enrollment trends, birth data from the state Department of Public Health and local trends.

His numbers show Preston's preschool through eighth-grade enrollment could grow by about 5 percent to about 460 students from 2015 through 2025, but he also reported a statewide K-eighth-grade enrollment drop of 13 percent. Prowda concluded in his Preston projection: “I consider the projection may be very slightly optimistic.”

Superintendent John Welch said the district asks Prowda to update his enrollment projections each year. Overall, the district expects a stable enrollment in the coming years, Welch said, not the sharp drop predicted elsewhere.

Between 2010 and 2015, Connecticut's population of school-aged children decreased by 3.46 percent, the sixth highest rate in the nation, according to data from the U.S. Census. By 2025, the student population in Connecticut is projected to decline by nearly 10 percent to 631,241 students, according to data from the Connecticut State Data Center.

Experts link decreasing student enrollment to a variety of factors, from a decline in the state's birth rate, as people have fewer children and have them later, to people leaving the state for job opportunities.

The enrollment cliff Preston experienced a decade ago changed the school landscape in town. The Poquetanuck and Preston City School elementary schools closed and were consolidated into the new Preston Veterans' Memorial School in 2003. Both former schools were demolished.

In the proposed 2016-17 budget, Welch listed projected enrollment at PVMS at 293 students, with a school capacity of 450. Enrollment at Preston Plains Middle School is projected at 144, with a school capacity of 200.

Preston officials continue to discuss whether to consolidate all students to the newer PVMS, but thus far, the talks haven't reached a conclusion. Welch said there is surplus classroom space at each school being used for other school functions, but neither building has rows of unused classrooms.

One big question in planning Preston's school future is what development might come to the 393-acre former Norwich Hospital property being marketed for mixed commercial and residential development.

“When they figure out what to do with it, that will give a better idea of what will happen with the schools,” Welch said.

Over the past 10 years, as Preston's enrollment has dropped from 479 in 2005-06 to 439 this year, the school budget has gone from $9.2 million in 2005-06 to $10.8 million this year. For five consecutive years from 2008-09 through 2012-13, the budget remained flat at $10.4 million. The budget stayed at $10.8 million for the past two years, but a special education increase is contributing to a proposed increase next year to $11.4 million.

The region's growing number of magnet and charter schools has tapped into Preston's K-8 enrollment somewhat in recent years. In 2014, Preston public schools enrolled 89.5 percent, 418, of school-aged town children. Another 28 students attended non-public schools, 17 attended magnet schools and four attended “other public schools,” according to Prowda's report, using the latest available state data.

Welch said those numbers are about the same this year.

“It's always been a relatively small population,” Welch said of families opting for other choices. “We did see an uptick in the number going to magnet schools when the Marine Science Magnet High School opened. Those kids would have gone to (Norwich Free Academy).”

c.bessette@theday.com