Each year, more children — nationally and locally — are identified as having some form of autism.

Children with autism are in every school district in Rhode Island. And, the total in special education has been escalating. In 2003, the total was 653; in 2006, it was 1,139. In June, 2009, it hit 1,598.

Three classifications — classic autism, Asperger’s syndrome and pervasive developmental disorder not otherwise specified — are the most common disorders along the autism spectrum.

Asperger’s syndrome is considered the mildest form of autism, one in which the individual may not use common nonverbal behaviors, such as maintaining eye contact in social situations; or may not share joys or interests with others. These individuals are often exclusively preoccupied with a single interest or object.

Unlike other types of autism, individuals with Asperger’s show no delay in language development, have normal intelligence and age-appropriate self-help skills. With broad vocabularies, their “speech patterns make them seem like little professors,” according to the National Institute of Neurological Disorders and Stroke.

They generally struggle in social settings and appear somewhat clumsy or uncoordinated. It’s five times more common in boys than girls.

In 2007, the federal Centers for Disease Control and Prevention in Atlanta concluded, after a review of research and its own study, that 1 in every 150 children has some form of autism.

Prior to that, it was generally thought that the rate in the United States was closer to a range of 2 to 7 per 1,000 children.

“We don’t know what the increase is due to,” said Amanda Aldrich, a CDC spokeswoman.

“There is better diagnosis. We also changed the definition quite a while ago and expanded it, so more children were falling under it.”

But, Aldrich adds, it is possible that there is an actual increase in the number of children with autism, not just an improvement in identifying them.

Stephen J. Sheinkopf, a research psychologist at the Brown University Center for the Study of Children at Risk and the acting research director at Bradley Hospital’s Center for Autism and Developmental Disabilities, agrees. “I think the uncontroversial understanding is that many more people now are diagnosed with the conditions than used to be diagnosed with the conditions, but whether that means there has been a true increase in prevalence is not readily answerable.”

Earlier this month, medical researchers for the U.S. Health Resources and Services Administration set the rate for boys at 1 in 58, and for boys and girls together at 1 in 91.

Using information from a 2007 National Survey of Children’s Health, the researchers surveyed by phone some 78,000 parents of children, ages 3 to 17, to ask if they had ever been told that their child had an autism spectrum disorder.

Sheinkopf, in a letter to Pediatrics, the journal of the American Academy of Pediatrics, where the research was published Oct. 5, advised those in the field to be “very cautious” about using the findings to estimate autism prevalence because of the form of the questions and because none of the children counted were seen in person.

mmckinne@projo.com