LONG ISLAND – Enrollment at Long Island School has fallen to just 10 pupils, and some islanders fear the decline is because rising property values are making the island unaffordable for families with young children.

The school, which serves kindergarten through grade five, had 11 pupils last year but has typically had between 16 to 24 children a year for about two decades, said Paula Johnson, lead teacher at the school.

The school population on the Casco Bay island has risen and fallen over the years with birth cycles. But this time islanders fear the number is going down because of the rapid upward climb of real estate prices.

Islander Shawn Rich, 36, a fisherman whose 4-year-old daughter, Zalea, is in kindergarten, said he has brothers who no longer can afford to live on the island where they grew up. Small cottages without a water view are selling for $200,000, he said, and homes on the water go for half a million or more.

With those prices, it’s tough for young families to afford to live on the island, Johnson said.

“We desperately need children,” she said.

Long Island, which seceded from Portland in 1993, has a year-round population of about 300 people, which swells about fivefold in the summer. It is about three miles long and less than a mile wide.

Even with declining enrollment, islanders hope the quality of the education on the island will serve as a drawing card for families with children. On the first day of school on Friday, many of the amenities of the small school were evident.

One is its warm, close-knit atmosphere. Parents and other proud relatives such as grandparents come to school with their children on the first day to share refreshments, chat with staff and each other and attend an informational session about the upcoming year.

It seemed like a big family reunion on the school’s lawn, as the adults milled around in the warm September sun and the pupils posed for class pictures.

The school building was built in the 1940s, according to Chub Dowdy, 73, who said the island had two schools when he was growing up, one at each end of the island and each with about 40 pupils.

But now the building has a beautiful new 4,000-square-foot addition, about 11/2 times the size of the rest of the school.

Islanders held a variety of fundraising activities to cover its $850,000 price tag. It contains a library, a computer room and a community room with a stage, all for use by both pupils and residents.