Wendy Grunthal teaches first graders about Israel Wednesday Dec. 14, 2011. Grunthal is the newest first grade teacher at Prairie Ridge Elementary. The school currently has 65 students in first grade. (Lewis Geyer/For Longmont Weekly) ( LEWIS GEYER )

LONGMONT -- Prairie Ridge Elementary School principal Kirsten McNeill received an unexpected surprise this fall: 49 more students than expected, mostly in first and second grades.

The increase put 34 students in one first-grade class and 33 in the other, and 28 in the second-grade classrooms. Typically, first-grade classes in the St. Vrain Valley School District have between 20 and 28 students, according to the district.

Fortunately, the situation changed pretty quickly. Teacher Wendy Grunthal transferred from another school in the district so Prairie Ridge could add a third classroom for first grade.

"The district really did well with reshuffling," McNeill said.

Prairie Ridge, with 12.4 percent growth since 2010, was the fastest-growing traditional school in the St. Vrain Valley School District, according to the 2011 enrollment report presented to the school board on Wednesday night.

Overall, the district's enrollment increased 2.64 percent to 27,193 students, including those enrolled in charter schools.

Charter schools saw growth of 16 percent, or 417 students, with the openings of Aspen Ridge Preparatory School in Erie and Twin Peaks Charter High School in Longmont.

Traditional public school enrollment increased 1.17 percent, or 282 students.

As has been the trend for several years, most of the growth is in the eastern and southern areas of the school district.

Mead High School, which has its first senior class this year, pushed enrollment in that feeder system up 10.3 percent since last year. A feeder system is the elementary and middle schools that are associated with a particular high school.

Enrollment increased in the Frederick feeder system, which includes Prairie Ridge, by 3.9 percent. The Erie feeder system, which includes the newly opened Red Hawk Elementary in Erie, saw an increase of 2.2 percent.

In Longmont, only the Silver Creek feeder system saw an increase, with 0.8 percent more students.

Enrollment dropped slightly -- 0.4 percent -- in the Skyline feeder system, according to the report.

Longmont High School's feeder system enrollment fell 2.1 percent.

The greatest enrollment drop was in the Niwot feeder system, where enrollment fell 2.4 percent.