Holy Trinity School has been serving East Honolulu for 49 years, but must increase enrollment substantially — and soon — to reach the half-century mark.

Enrollment at the private K-8 Catholic school, along Kalaniana'ole Highway, has been declining for the past few years, but officials say this year's decrease has been the most significant. Just 81 students are registered for this year, compared with an average of 110 to 130 students in previous years.

"The enrollment is down because of the economy — that's one reason," said principal Sister Rose Schillinger, who started her teaching career in Hawai'i at the school in 1983. "Some of our parents have lost their jobs, some are moving back to the Mainland."

Holy Trinity is among a number of private schools that have reported declines in enrollment as the new year begins.

Catholic elementary schools in particular have a difficult challenge, Carmen Himenes, superintendent of Hawaii Catholic Schools, has said.

An estimated 39,555 students in Hawai'i were enrolled in private schools last year, while 172,364 attended public schools.

The drop in enrollment at Holy Trinity comes despite annual tuition well under that of many other private schools — $5,250.

The school hopes to gain about 20 additional students by the end of September to survive the difficult economic times.

Although classes began Monday, the school will continue to accept students as the year progresses.

"We really feel quite certain that we're going to make our hundred for this year and 120 for the next year so that we celebrate our 50th anniversary," Schillinger said.

The majority of the school's students come from the Hawai'i Kai area, and some receive financial aid ranging from $1,000 to $4,000 based upon need. The school also has an adopt-a-student program where anyone can sponsor an anonymous child and contribute toward their tuition.

After students graduate from eighth grade, they can usually get into any school of their choice because of the school's perennially high test scores, Schillinger said. Most students continue their education in private schools, she said.

The school has a 10-to-1 student-teacher ratio and offers a wide range of educational opportunities, Schillinger said. Besides the core academic subjects, the offerings include computer classes, Japanese language instruction, art, physical education, band and competitive sports.

"Right now, the band has become the main focus," Schillinger said, noting that six students completed a 12-day trip to Australia in conjunction with World Youth Day 2008 in July.

Among the school's 18 employees is author Shelly Mecum, who collaborated with paralyzed artist Peggy Chun to create the book "The Watercolor Cat." Holy Trinity students also aided Chun in creating a mosaic of Father Damien that was revealed in March at the state Capitol.

"They're (the students) always doing amazing things because they do it with God's love," said Mecum, who teaches language arts, social studies and religion to students in grades six through eight. "It's a school driven by social justice."

Yesterday, Mecum and two other teachers were facilitating activities based on the medieval period with the middle school students in the school's newly renovated gym. Through donations and volunteer efforts, the gym was refurbished this summer at no cost to the school.

"For our school's motto, we have 'Living God's Love' and that permeates throughout the whole school every day," Schillinger said.