In the last decade, Maine’s youth population dropped by nearly 10 percent. As a result nearly every school district in the state has fewer students. This decline is predicted to continue for at least the next two decades.

Yet spending on K-12 education continues to increase, putting these two trends on a collision course.

“Over the next 20 years we’re looking at K-12 enrollment going down, absolutely,” said Laurie LaChance, director of the Maine Development Foundation, which researches Maine education and its effects on the state’s economy.

“That will touch the entire system,” she said, explaining that those fewer young people will grow up and likely have even fewer children. “It strikes at the heart of why we have to rethink this.”

According to U.S. Census data, Maine’s population of infants to 14-year-olds dropped by 9.5 percent from 2000 to 2010. That is a total loss of more than 23,000 kids. The biggest drop was in 10- to 14-year-olds.

To put that in perspective, Maine’s youth population dropped more than the total populations of Rockland, Rockport, Camden and Belfast combined — all in a decade. And experts say those numbers will continue to slide.

Meanwhile the population of 45- to 69-year-olds jumped 30 percent in the same 10 years. That jump was from about 365,800 to 475,700 — an increase of about 110,000. That leap is equivalent to adding Portland and Bangor’s populations to that age group.

There are several factors involved with the changes in the youth population, according to Amanda Rector, the state economist. One factor is migration in and out of state. Another is age.

“An older population has fewer children, and Maine’s lack of racial diversity also contributes to a low birth rate,” Rector said. White families tend to be smaller than Hispanic families, for instance, she said. With fewer babies, Maine has fewer schoolchildren.

Maine lost about 5 percent of its school-age children in just four years. In 2006, Maine had 202,240 students enrolled in public schools. By 2010, that number dropped to 192,202. The 2011 numbers are not in yet.

Every school district has seen fewer students in that time period, except eight: Machias Bay Area, Orrington-Dedham, Auburn, Lewiston, Houlton, Berwick, South Portland and Wells-Ogunquit. This doesn’t include a few island and Indian schools that have very small student populations. It also doesn’t include nonconforming school districts — districts that didn’t comply with the state’s consolidation law or were too small to be required to — for which data is harder to access.

Of the school districts that lost students, the decline typically was fewer than 200 students. Brunswick was one exception and it closed two schools this school year, but that was because the Navy base closed and it lost 650 students.

LaChance of the Maine Development Foundation has studied the trend of decreasing student enrollment as it relates to school budgets. If Maine keeps doing what its doing, the state will be on a dangerous path, she said.

For the 2000-01 school year, total statewide K-12 spending was just under $1.5 billion, according to figures from the Department of Education. That includes state funds, known as general purpose aid to education, and money raised locally through property taxes, as well as federal funds. By the 2009-10 school year, total spending had risen to slightly more than $2 billion. The state share was $921 million.

As a result, per-pupil spending has grown rapidly. In 2000-01, the average K-12 per-pupil cost was $6,233. By 2009-10, it had risen to $9,663, according to the department’s numbers. Although the increases have slowed in the last two years, the average increase over the decade was 5.2 percent.

“The biggest budget item at state and local government is K-12 education. As enrollment goes down, people will ask the question, why are we spending more dollars on a system that is serving fewer kids. They should ask that question,” she said.

The answer is this, according to the Maine Department of Education: Yes, student enrollment is going down. Yes, the state budget for education keeps rising at about 2 percent a year. But it’s more complicated than that, said Maine Department of Education Deputy Commissioner Jim Rier, an expert on school finance.

“The cost of education [equation] has a component that is driven by the number of students, but there are many other components driven by numerous other things: special education and inflation, for instance,” Rier said. “In spite of lower enrollment, the net overall cost of education keeps growing. You could argue they would grow more if the population wasn’t declining.”

The declining enrollments in the past years have “moderated the amount of state support” for schools — just not enough to negate other costly parts of running schools — such as employee health insurance and heating oil — that keep getting more expensive.

At an education forum in Rockland earlier this month, Maine Department of Education Commissioner Stephen Bowen spoke about his budget.

“There is no more money. We don’t have any more money in the state. The feds are broke. Property taxes can’t bear it. We have to figure out how to do more with less,” he said.

He then touted a high school model that integrates local community colleges and vocational schools to share one roof. It’s economies of scale: The more students one building serves, the more efficient it becomes.

Many small communities hear such talk as a threat to close local schools. And while more and more communities are considering closing small schools, often they vote to keep them open.

The most recent example was in Monroe. The RSU 3 board voted earlier this week to keep open the town’s elementary school, which serves only 54 students. Through the state’s school funding formula, the school unit this year gets 68 percent of its funding from the state. This means taxpayers across the state are largely footing the bill to keep the school open.

“It’s terrifying for a community to face the closure of a school — it’s at the heart of many communities. I’d encourage all of us to think of consolidation differently,” said LaChance.

She proposes an idea similar to Bowen’s, but at the other end of the school timeline: When too many children leave a school and it creates extra space and extra staff, add pre-kindergarten services. Instead of closing schools and upsetting communities, why not use the buildings that are there and suddenly have more space to add pre-K programs, LaChance suggested.

One district that’s already doing this is Orrington. That district is one of eight in Maine that is growing, although only slightly. It’s because in the last three years, the district saw a shrinking student population and decided it had the space and teachers to add pre-kindergarten with 35 young students. If not for those 35 preschoolers, Orrington would have been with the other districts — it would have lost 16 students total. Instead, it will get extra state funding.

“If we didn’t have the pre-K our population would have dropped,” said the local superintendent, Allan Snell. Had the district’s population dropped, Snell said he may have had to cut a teacher position. Instead, he kept that veteran teacher and added two education technicians.

“I would say it maintains the same level of funding with the cost of an additional ed tech,” Snell said.

Of the other seven Maine school districts that didn’t lose students in the past few years, most added pre-K programs. Lewiston added about 250 students from 2006 to 2010. That includes almost 200 new pre-K students. Houlton’s 90 new pre-K students diverted what would have otherwise been a loss in students for the district.

Four-year-old programs are one of the only things helping curb school enrollment drops, according to the Department of Education’s Rier. In 2006, Maine had about 1,500 4-year-olds in public school pre-K programs. In 2010 that had jumped to about 3,900 4-year-olds. About 20 districts added pre-K programs in that time, bringing the total to about 170 districts with 4-year-old programs.

“They become part of schools sooner,” Rier said. “That’s new to the mix.”

While pre-kindergartens have helped boost enrollments in many districts, for now, the youth population will continue to drop and Maine will face difficult decisions about how it educates its children.

“The costs have gotten out of line, it’s unsustainable. We have to reassess how can we deliver these [services] more efficiently,” LaChance said.