At Knightsville Elementary, the biggest elementary school in the state, two of every five students attend classes each school day in trailers, and it's just getting bigger.

However, this could be the last year the mobile units take up space on the campus.

Thanks to 2012's $179 million bond referendum, Dorchester District 2 expects to open three new elementary schools next year, each with a capacity of 1,000 students, providing some relief for Knightsville and other overcrowded schools, like Beech Hill and Reeves. The referendum also provides for a new middle school, set to open in 2016, and renovations to several other schools.

Dorchester District 2 leased 11 new trailers this year to ease overcrowding, bringing the district's total to 198, but none of the new trailers went to Knightsville, which grew this year by another 40 students.

"There are a lot of kids here, but it's so organized that you don't even notice," said school volunteer Kim Boyea, who is also PTA president.

The building, constructed in 1938, has room for only 850 students, forcing about 600 others into the 31 mobile units that have been added over the years.

Other schools in the Lowcountry are overcrowded, too, but none as much as Knightsville. In Charleston County, Pinckney Elementary and nearby Laurel Hill are both about 200 students over capacity. The Charleston County School Board is preparing to put a referendum before voters to build new schools.

In Berkeley County, several elementary schools, including Sangaree, College Park and Hanahan, are over capacity. That district got voter approval in 2012 to issue bonds for $198 million to build three new elementary schools, a new middle school and a new high school and renovate other schools.

Knightsville's overcrowding - and the addition of 15 new teachers districtwide instead of the 25 Superintendent Joe Pye requested - means more pupils per classroom, Pye said.

The school has been overcrowded for more than a decade, adding trailers each year as the enrollment kept growing. Most classes will have one more student than they had last semester, Pye said. Class sizes at the start of the school year are kindergarten, 26; first grade, 19; second and third grades, 22; and fourth and fifth grades, 26.

"Will it affect test scores? Probably not, not if it's in the short-term," he said. "We're just asking people to hold on while we get these new schools out of the ground."

Pye said his goal is to bring the school's attendance back to 850. The new elementary schools are on track to open during 2015, said district capital improvement facilitator Bob Folkman.

While they wait, parents have resigned themselves to the conditions, officials said.

"I haven't heard any complaints (about overcrowding)," said Pye. "I think they all know we passed the referendum and we are anxiously trying to get some new schools together, so they are waiting for that to happen."

Sand Hill Elementary, six miles away from Knightsville on Summers Drive on the East Edisto tract, is expected to pull some of the students who currently go to Knightsville. The attendance lines have not been drawn yet.

Knightsville, on Orangeburg Road, draws students from growing neighborhoods like Huntington Farms, Sunburst Lakes, The Ponds and White Gables.

"Knightsville seems to be one of our schools that tends to never lose students," Pye said. "They will probably have 50 more students (than last year) by Christmas time. That would normally be two more classrooms, but we are out of space."

The situation could be worse, Pye cautioned. In 2007, the district opened William M. Reeves Jr. Elementary two miles from Knightsville. That school grew by more than 100 students to nearly 1,200 this year.

"That's 2,600 kids," Pye said. "Had we not built Reeves, all of them would have been zoned for Knightsville."

The crowded conditions have led to other concessions.

"They have learned to use every bit of space they have," Pye said. For instance, special area teachers go from classroom to classroom to teach, pushing their belongings along on a cart.

To get all the students home, seven bus routes have to be run twice each afternoon, meaning about 400 students wait as long as an hour at the end of the school day in Knightsville's computer labs, media center or hallways for their bus to return to pick up the second load. Durham School Services, which runs the district's buses, is working on a solution, Baird said.

That's not the first time the district has had to resort to that. Fort Dorchester also had to run double routes in the year before Pye Elmentary opened and relieved its overcrowding.

Reach Brenda Rindge at 937-5713 or @brindge on Twitter.