But it does benefit parent-child interaction, the study, which was also published in the journal The Lancet, shows.

The story is kind of mixed -- positive and disappointing, said Dr. Jonathan Green, of the University of Manchester, who worked on the study.

Autism spectrum disorders affect about 1 in 100 children and cost healthcare systems billions of dollars each year. Green said neither behavioral nor drug treatment had been very successful at improving autistic symptoms, such as poor social skills, slow language development and repetitive behaviors.

But a few smaller studies had suggested that communication-focused treatment -- based on recent insights into autism development -- might be effective.

So Green and colleagues assigned 152 autistic preschoolers randomly to receive either this treatment or standard care. Throughout a year, they held language-therapy sessions for the treatment group, in which parents learned to adapt their communication to their kids' impairment.

After one year, they compared the two groups of kids, measuring their symptoms with a widely used test. The treatment turned out not to be effective when accounting for group differences such as age and treatment center.

The way we designed the trial was to give the treatment a stiff test, Green told Reuters Health. We didn't find what we hoped for.

Yet children communicated more with their parents after the treatment, said Green, adding that parents reckoned that the treatment had done a very good job of shifting their children's symptoms.

Audrey Thurm, a child psychologist at the US National Institutes of Health, said the new research was more trustworthy than earlier studies.

We have very few studies that are as rigorous as the study that just came out, she told Reuters Health.

She added that most US children with autism get treatment similar to the one tested by the British researchers, and that the results should deter such efforts.

For one, she said, in child-parent interactions, they did find meaningful changes. And for another, some children may respond well whereas others might not, canceling out a potential effect.

Autism is a hard nut to crack, said Green. We've got ways to go yet.

Autism