Pediatricians often fail to take seriously parent concerns about autism, new research suggests, sometimes delaying children from receiving a diagnosis and treatment for years.

In a study looking at the experiences of children diagnosed with autism as compared to those with intellectual disability and developmental delay, researchers found that doctors were 14 percent less likely to take a proactive approach when families cited concerns about autism.

Rather than refer children to specialists or for developmental testing, the study found that pediatricians often reassured parents worried that their child might be on the spectrum or indicated that their child “would grow out of it.”

“This study implies that the behavior of health care providers is likely a very important factor in delayed autism identification,” said Katharine Zuckerman of Oregon Health & Science University who led the study published online this week in The Journal of Pediatrics.

For the study, Zuckerman and her colleagues looked at data from a nationally-representative survey of parents of 1,420 children with autism and 2,098 kids with intellectual disability or developmental delay.

Parents of those later diagnosed with autism said they expressed concerns to their health care provider about their child’s development around age 2, a whole year earlier than moms and dads of kids with other delays. Nonetheless, among families surveyed, children with autism were not diagnosed until age 5, on average, even though kids with the developmental disorder can generally by identified by age 3.

Significantly, the study found that children whose doctors were passive about initial autism concerns waited as much as two years longer to be diagnosed as compared to those whose health care providers were immediately proactive.

“We know that early identification of ASD is beneficial to children and their families. Unfortunately, many families experience long delays between when they first have concerns and when their child gets diagnosed with ASD,” Zuckerman said.

The findings, researchers said, indicate that doctors may need more education and training to better respond to parent concerns related to autism in particular.

Currently, the American Academy of Pediatrics recommends that doctors conduct developmental screening at 9, 18 and 30 months with all children as well as autism-specific screening at 18 and 24 months.