CAPITAL REGION — Enrollment in Capital Region schools is relatively flat or declining, although districts such as Shenendehowa and Schenectady are bucking that trend.

Demographic experts say one reason for the decline is that children born in a small birth-rate spike in the late-1970s and early 1980s are completing high school. School officials throughout the region say suburban districts are the ones hardest hit.

For example, in the Scotia-Glenville School District, the total enrollment as of Sept. 5 was 2,793, down 74 students from last year, according to district spokesman Robert Hanlon. This breaks down to 1,186 in elementary schools, 653 in middle schools and 954 at the high school.

Hanlon said the downward trend has occurred as fewer students entered kindergarten than those who graduated the previous June.

Elementary school enrollment had been climbing for the past few years but has recently flattened again.

The district has about 250 fewer students now than it had in 1999. Hanlon noted that Scotia-Glenville is not alone. Most schools throughout the Capital Region either have decreasing or flat enrollment.

A sharply lower birth rate is one reason for the trend. Leif Engstrom, program manager for the Capital District Regional Planning Commission, said birth rates declined sharply between 1965 and 1971 in New York and stayed at a low level in the early 1970s. Those women in the early 1970s gave birth to fewer children than in previous generations and are now moving past childbearing age. This affected enrollment.

Since that big dip in the early 1970s, the population has risen slightly. There was another, smaller spike in the late ’70s and early ’80s, and those children are now of high school or college age.

“That’s why local colleges are tripling up dorm rooms that were only intended for two students,” Engstrom said.

The smaller spike was followed by another dip in births after the early 1980s, Engstrom said.

He said declines in enrollment have been moderate and for the most part have not required mass closings of schools. Schools probably will not need to lay off teachers, but may not fill retirements until enrollment ticks up again.

Engstrom anticipated the population of the Capital Region would stay relatively stable. It has a strong base of employment with government, health care and emerging technology businesses. Eventually, school enrollment will climb again as baby boomers retire from these positions and are replaced by younger workers with families.

Districts such as Amsterdam are growing modestly. Superintendent Thomas Perillo said enrollment is about 3,780, up from 3,740 last year. There are 1,737 in the elementary school, 1,231 in the middle school and 812 in the high school.

“There’s never been a real huge jump,” he said.

The Albany School District’s public schools have been losing students with the proliferation of charter schools — nine at last count.

“We’ve seen a steady trend downward,” said spokesman Ron Lesko.

The district’s enrollment this year stands at about 8,204, a drop of about 400 students from last year. At the start of the 2000-01 year, the district had more than 10,000 students.

Districts in which there was a housing boom have grown. Shenendehowa spokeswoman Kelly DeFeciani said enrollment there is around 10,000 students, but she said that number is likely to decrease in the coming weeks. Frequently, people move out of the district and do not notify school officials.

This breaks down to 4,652 elementary school students, 2,254 middle school and 2,999 high school students.

DeFeciani said the school district has been growing pretty consistently, at a rate between 50 and 100 students a year since 1984. She attributed the increase to residential growth. But the housing market has softened, she noted.

“The projections are that we’re still going to grow, but the growth is going to slow down,” she said.

In the past few years, the district has built a high school addition, a new elementary school and a new middle school to accommodate the growth.

The Schenectady City School District is an urban district that is also bucking the trend of declining enrollment.

Since 1991, the district has grown anywhere from 1 percent to 4 percent annually, except for one year when enrollment dropped a tenth of a percent.

Superintendent Eric Ely attributed the increase to affordable housing. Ely said about 500 to 600 returning students are attributable to the closed International Charter School of Schenectady. There have been new students as well.

During the past decade, a number of Catholic schools have closed in the area. In 2004, there were five Catholic schools in the city. Today there are two.

Ely said since the economy has worsened, perhaps people are looking to lease and rent more. Also, as the cost of fuel has increased, people may look to move closer to cities.

“Traditionally, as the economy declines, enrollment in urban districts increases because of those factors,” he said.

The district is forecasting it will grow at a rate of 1 percent to 2 percent in the coming years, which will not impact any one school, as the district is spread over 14 buildings. However, the district is exploring options for a new school. The population growth seems to be concentrated in the Mont Pleasant neighborhood and north end of the city.

The population of the lower grades is somewhat high, Ely said. There are 877 kindergartners, 842 first-graders, 821 second-graders, 775 third-graders and 784 fourth-graders. Assuming that “bubble” moves through the system, he said, the district has to start taking a look at the size of its buildings. It only has five-year nonrenewable lease agreements with the Albany Catholic Diocese for the facilities it is using at Katharine Burr Blodgett and Franklin D. Roosevelt schools.

“We have to come up with a plan sometime in the next year so we have an answer when those leases expire,” he said.