Arlington County Public Schools is planning to build two new elementary schools -- the first new schools since the 1990s -- to handle the booming enrollment that's straining the small district.

Superintendent Pat Murphy also is proposing several projects to add space in existing schools in her $537.7 million, 10-year Capital Improvement Plan. While past plans have focused on the upkeep of aging buildings, school officials say this is the first plan to build capacity that Arlington has ever put forth.

The county has good company in neighboring school districts like Fairfax and Montgomery counties, which are perpetually planning and building new schools to keep up with an influx of students.

Arlington's 32 schools serve 22,676 students, an increase of more than 2,000 over last school year. Seventeen schools -- 15 at the elementary level -- are already over capacity, filled with more students than they were built for. Within five years, enrollment is expected to near 27,000 students.

"We haven't opened a brand-new school in many years," said Alison Denton, the school system's facilities planner.

In 2000, Arlington moved Carlin Springs Elementary students into a new building, but Denton said the most recent brand-new school came some time before then.

While Fairfax and Montgomery have seen enrollment growth stem from the higher birth rate of their ballooning Hispanic populations, Arlington's growth is driven by single-family homes. Denton said she believes there is a generational turnover afoot in which older residents are leaving and younger residents with small children are moving in.

"All signs are pointing up," she said.

One of the new elementary schools would be near Williamsburg Middle School by 2015, adding 600 seats. The other would be completed in 2017, also adding 600 seats, near Carlin Springs Elementary and Kenmore Middle School.

School officials are also planning projects that would add 12 classrooms, or 225 seats, at each of three elementary schools: Ashlawn, Arlington Traditional and McKinley.

"I believe these changes will enable [Arlington] to provide much-needed instructional space while continuing to maintain existing facilities that meet the needs of our students and teachers," Murphy said.