Updated March 26, 2015.

Common knowledge says that parents whose child has been diagnosed with autism should run -- not walk -- to the nearest therapist. Early intensive intervention, it is said, is the key to "optimal outcomes" for autistic children. Scientists have long known that the brain grows quickly between the ages of zero and three, which suggests that early intervention would be an ideal way to treat a childhood disorder.

But is there any evidence that this is really the case?

Early Intervention Is Common Sense

It makes sense to treat an autistic child as early as possible. The reasons, though, are not research-based: they're simple common sense. Preschoolers have no other obligations, so their whole day can be devoted to therapy (as opposed to academics). Two-year-olds have few ingrained habits, so it's relatively easy to stop negative behaviors before they become intractable. And very young children are ... very young children. Even in the grocery store, bad behaviors can be tolerated. Once a child is nine or ten, tantrums in a store are simply unacceptable.

Early Intervention Works

There's no doubt that autistic children who undergo intensive intervention, be it behavioral or developmental, do better than children who don't. And there's certainly no good reason to wait to provide such therapy.
How well does such therapy work? That depends upon the child. As each individual child has his own profile, abilities, and challenges, each child will have his own outcomes.

But even a little progress is far better than none, especially when that progress comes in the form of new communication skills that allow a child to express his desires and needs.

No Evidence That Earlier = Better

While there are solid practical reasons for early intervention, there are -- so far -- no research studies that show that earlier intervention offers more hope of improvement than later intervention. In fact, Geraldine Dawson, Ph.D., Professor of Psychology and Director of the University of Washington Autism Center, makes the following point: "For all we know, a child with a developmental delay may have a longer window of opportunity for growth. I think it's not helpful to alarm parents in that way. I've seen kids who start late and quickly catch up -- a lot of kids with intensive early intervention who progressed slowly and then took off in elementary schools."

The Bottom Line: Walk, Don't Run, to Early Intervention

Early intervention is clearly a good idea. But it's by no means clear that the earlier and more intensive the intervention, the better the outcome. Parents who rush to early treatment with the hope that their child will quickly "recover" from autism may be disappointed -- while parents who waited "too long" may see surprisingly positive outcomes.

References

Interview with Geraldine Dawson, Ph.D., Professor of Psychology and Director of the University of Washington Autism Center. January, 2007.
Dawson G, Toth K, Abbott R, Osterling J, Munson J, Estes A, Liaw J. Early social attention impairments in autism: social orienting, joint attention, and attention to distress.Dev Psychol. 2004 Mar;40 (2):271-83.

Dawson G, Zanolli K. Early intervention and brain plasticity in autism.Novartis Found Symp. 2003;251:266-74; discussion 274-80, 281-97

Matson JL. Determining treatment outcome in early intervention programs for autism spectrum disorders: A critical analysis of measurement issues in learning based interventions.