Close to half of all teenagers with an autism spectrum disorder are bullied at school, says a survey of their parents.

The results, published Monday in the Archives of Pediatrics & Adolescent Medicine, suggest that rate is much higher than the estimated 11 percent of bullied kids in the general population.

Previous studies have found kids and teens who are bullied tend to be more depressed, lonely and anxious and do worse in school than those who aren't picked on, according to the researchers.

That means bullying could make things extra difficult for those with autism, who may already struggle more in school than other kids.

The researchers say the findings suggest schools should target their anti-bullying campaigns toward the more vulnerable populations, such as children with autism and attention deficit/hyperactivity disorder (ADHD).

"I would argue that the bullying interventions that we're using now, if not tailored, are ineffective," said Paul R. Sterzing, the study's lead author from the University of California, Berkley.

He added that the problem may also grow along with the number of kids being diagnosed with autism. It's now estimated that about one in 88 children in the U.S. has an autism spectrum disorder, which include autism and Asperger's syndrome.

Using records from a 2001 survey of 920 parents, Sterzing and his colleagues found that 46 percent of parents said their autistic teenagers were the victims of bullying and 15 percent thought their children were bullies themselves. Nine percent of moms and dads said their kids were both victims and bullies.

While the researchers said autistic children were picked on at a much higher rate than current estimates for kids in general, the proportion who were bullies or both victims and bullies was about average.

Sterzing told Reuters Health that teens with autism and ADHD or those who had autism and were in regular classes were both especially likely to be victims of bullying.

That, however, does not mean kids with autism should be separated from their peers and put in special education classes. Instead, Sterzing said it could mean that regular classes haven't been doing a good job of including kids with autism.

Debra J. Pepler, who researches bullying among vulnerable children at York University in Toronto but wasn't involved in the new study, told Reuters Health there are some strategies that may help reduce bullying toward autistic children.

Specifically, she said classes can create "circles of support," which are groups of children who are educated about a student's condition and able to provide help and support.

She added that it's important to set the expectation for the classroom "that everyone has the right to be safe, and just because someone is different doesn't mean it's OK to make fun of them or bully them."