A rigorous, if small, study of behavior treatment found two years of therapy can vastly improve symptoms in autistic children as young as 18 months and often results in a milder diagnosis.

Early autism treatment remains controversial because there's been little evidence that it really works. But there's also a growing emphasis on diagnosing autism at the earliest possible age.

The therapy focused on social interaction and communication. Therapists or parents would repeatedly hold a toy near a child's face to encourage eye contact, which is a common problem in autism. Or they'd reward children when they used words to ask for toys.

Children in a group receiving 25 hours of treatment a week registered an average IQ gain of almost 18 points after two years. Language skills also improved. However, no children were considered "cured."

The study was published online today in Pediatrics. One autism education specialist calls it "a landmark of great import."