There is plenty of evidence that autism is being diagnosed much more frequently in pre-school children, but surprisingly little evidence that anything effective can be done about it. Until now most intervention studies have shown only short-term improvements, and some of these involved highly intensive therapist input.

The first study to show sustained benefit from an early intervention received considerable mainstream media attention. The original PACT study, published in 2010, recruited children aged 2 to 5 years who fulfilled internationally recognised criteria for autistic spectrum disorder (ASD) diagnosis at three major UK …