Gov. Bob McDonnell (Alexa Welch Edlund/Associated Press)

McDonnell (R) had originally signed a bill into law last spring mandating coverage, but Attorney General Ken Cuccinelli (R) determined that the legislation contained imprecise language that legislators needed to correct.

Since then, families who expected insurance coverage have continued to pay out of pocket — if they can afford it — or forgo treatments they say could help their children learn basic skills such as walking and talking.

The bill will require health insurers to pay for specialized treatment — called applied behavioral analysis — as well as occupational, speech and other therapies for children ages 2 to 6. The maximum benefit was capped at $35,000 each year.

“After years of hard work and coordination, hundreds of children will finally get the help they need to make a real difference in the treatment of autism spectrum disorders,’’ Del. Tag Greason (R-Loudoun). “I'm appreciative of all the help I've received over the last two years from my colleagues in the House of Delegates and advocates from across the Commonwealth.”

The bill directs the state to write regulations within 280 days for those who teach applied behavior analysis to autistic children. That means coverage should start by the end of the year.

Autism is a neurological disorder that affects one in 110 children and one in 70 boys, according to national statistics. Virginia does not keep statistics on autism, but the state Department of Education estimates that 11,700 autistic children attend school (many others are too young or not able to attend).

The original measure had failed for 11 straight years until House Speaker William Howell (R-Stafford) backed it — even though conservatives considered the measure an unacceptable mandate that would drive up insurance costs.

Thirty-four states and the District have laws related to autism and insurance, according to the National Conference of State Legislatures. At least 29 states require insurance coverage for autism treatment. Others require at least limited coverage.

There’s no estimate on the number of Virginia families who would benefit from the law, but it affects businesses that employ more than 50 workers and are not self-insured. Virginia set aside $1 million to cover state employees.