Montgomery County schools will expand autism services this fall, bringing new resources to high school students as the school system works to increase the range of programs available to an exceedingly diverse and fast-growing part of the special-education population.

The number of students diagnosed with autism in the county has risen dramatically in the past decade, from about 400 in the 2001-02 school year to just more than 1,900 by June 2012.

Students with autism make up about 10 percent of those receiving special education in Maryland’s largest school system.

“A lot has been changing,” said Kristin E. Secan, an instructional specialist for services for students with autism spectrum disorders. “And there is a lot going on.”

Autism is a developmental disability that can cause learning delays and social and communication difficulties. Symptoms vary widely.

Montgomery County and other school systems across the country have had to race to keep up with new diagnoses and wide-ranging needs.

Montgomery offers extra services to autistic students at their home schools. There are also special center-based programs to serve students with more severe or multiple disabilities. The county has a preschool program for children with autism and has tailored services for students diagnosed with Asperger’s syndrome, a specific and generally milder form of autism.

Two-thirds of all students receiving services for autism in Montgomery are taught in separate special-education classrooms for at least 60 percent of the day, according to a report released in January by Montgomery County’s Office of Legislative Oversight.

The high school services being introduced this fall are designed for higher-functioning students who are taking regular classes and pursuing regular diplomas, but who need modified instruction and extra help with social skills. The program builds on existing services available to middle-school students.

Participating high schools are Winston Churchill in Potomac, Watkins Mill in Gaithersburg and John F. Kennedy in Silver Spring.

School officials said they are training staff in the high schools this summer about appropriate social and behavioral support for autism. In the past year, they also trained hundreds of bus drivers and psychologists across the county to help them assess autism and respond safely and effectively to students with autism.

One challenge for educators in Montgomery and elsewhere is that research and best practices are still developing, along with the growing need for services.

The county’s report acknowledged that there is growing research about the issue, but concluded that “effective treatments for [autism spectrum disorders] remain a work in progress.”

Secan said the 147,000-student school system taps consultants and experts to help craft the best services. “With the increase in autism . . . we need to be able to build capacity for all our programs to better serve our students,” she said.