Over the past five years, enrollment at Campbell High in Ewa Beach has ballooned by nearly 800 students to more than 2,600, producing a severe shortage of classrooms and mounting stress on facilities at the aging campus.

And more growth is forecast.

Over the next four years, Campbell’s student body is projected to hit nearly 3,000 — 1,000 more than the school was built to hold.

Parents, teachers and lawmakers say overcrowding at the state’s largest public high school — and one of its highest achieving — is a growing concern, made worse because there is no long-term relief in sight.

"There’s not enough classrooms, not enough bathrooms, not enough athletic facilities, not enough rooms for kids to hang out at lunch," said Amy King, president of the Campbell PTSA, who added that the large enrollment also has its perks, such as a variety of academic programs.

"At some point it’s going to become a place where there isn’t enough elbow room."

Though the Department of Education is planning to construct a $6 million, 12-classroom building at the school, which is scheduled for completion in March, the new classrooms will make only a dent in the space shortage.

This year the school has 125 classrooms, 41 fewer than it needs, according to a Department of Education report.

In recent years the school has added several new portables, including one with rest­rooms only, but space on the campus for more portables is running out.

There is no time line to build a new high school — East Kapolei High — and plans for it depend on development that will likely be considerably delayed because of the economic downturn. It’s also unclear when the state might have the money for a new high school, which could cost upward of $120 million.

Randy Moore, Department of Education assistant superintendent of the office of school facilities and support, said there’s no doubt that a new high school is needed to relieve long-term overcrowding.

"The real question is, What do we do in this interim, which has an indeterminate length of time?" Moore said. "If a new campus is not on the horizon, we’ll simply have to keep adding more portables."

Campbell, established in 1962, isn’t the only high school over capacity, but its growth forecast makes its problems more acute.

The Ewa Beach school is projected to see a 12 percent increase in enrollment by 2015. 2 percent increase (or about 50 additional students).

Nationally, experts disagree about how much — or even whether — the size of a school affects instruction. But there’s no doubt that an overcrowded, and growing, school creates challenges for teachers and administrators.

Waipahu Principal Keith Haya­shi said overcrowding at his campus, which has 19 portables and five "temporary" buildings, limits the creation or expansion of new programs.

"Fortunately, I have really good teachers," he said. "They make do with what they have."

On the national scale, Campbell is not among the biggest high schools; several on the mainland top 4,000.

But Hawaii’s average enrollment for high schools is significantly larger than other states’.

Hawaii ranked fourth in the nation in 2008-09 for the average size of its secondary school enrollments, with 1,208 students.

The national average for secondary schools is 807, according to the National Center for Education Statistics.

(Hawaii also was above the national average for the size of its elementary schools, which on average have 534 students. Nationally, the average size of elementary schools is 475 students).

Board of Education policy says the optimal size for a high school is 800 to 1,600 students (on 45 to 55 acres).

Campbell is quickly running out of space, with 11 major buildings and an athletic complex on 38 acres.

The school’s growth is weighing on teachers and administrators, some of whom are worried that Campbell’s overcrowding could hurt student achievement.

An environmental assessment for the new classroom building at Campbell said the school’s "tremendous growth has resulted in overcrowded classrooms and other supporting facilities, staff shortages, and an overall reduction in the quality of the educational experience for students."

Campbell social studies teacher Corey Rosenlee said overcrowding makes a lot of things more difficult. During lunch there are often long lines in the cafeteria. Hallways are packed during passing periods.

But Rosenlee said the big problem is "there’s no relief in sight."

"They brought in portables the last two years. They’re building a new building. But what are they going to do in five years?"

Even as its enrollment has grown, Campbell has made big gains in student performance, becoming a model for other campuses. Partly because of its size, the school has been able to spend more money on teacher training and bringing in unique programs.

Today about 40 percent of the school’s students are enrolled in college prep or honors courses, and more low-income students take Advanced Placement exams than in any other Hawaii public school. The school’s test scores are on par with those in wealthier communities.

Jamie Dela Cruz, vice principal at Campbell, said one of the biggest concerns for administrators and staff is "trying to keep our students from being affected by the capacity issues."

He added, "The struggles that we have really are for normalcy and class size."

Though class sizes at Campbell are similar to those at other high schools — from 25 to 40 students — the classroom shortage means some teachers have no room of their own and must "float" to other rooms.

State Sen. Will Espero (D, Hono­uli­uli-Ewa Beach) said the continued growth of Campbell is a big worry and added the state should be considering some out-of- the-box solutions to help alleviate the school’s overcrowding, especially given the gloomy budget picture.

"If (enrollment) hits 3,000, that’s too big," he said. "Three thousand is a small college."

Education officials are informally discussing some other possibilities to help the school, including turning a nearby elementary school over to Campbell and shifting the elementary students to another campus.

The department also studied the possibility of shifting attendance boundaries to send more students to Kapolei and Wai­pahu high schools, but determined that wasn’t possible because both of them are already over capacity.

King, the PTSA president, said there are definite perks to a big campus: a plethora of programs and classes, more teachers and a greater efficiency to how resources are spent.

"You have access to resources. Less money is spent on facilities, and more money is spent on the classroom," said King, whose daughter is a senior at Campbell.

But the size does create problems, not least of which is the heavy stress on facilities — including electrical systems — because of so many students on campus.

"I don’t think we’ve reached the point of getting too big yet," King said, "but Campbell is getting close."