Update at 4 p.m.: McDonnell spokesman Jeff Caldwell said the governor will sign the bill.

The General Assembly has passed a bill — again — to provide insurance coverage for families with autistic children.

On the night before a key vote on insurance for autistic children, the Tidd-Heilner family toasts to "the passage of autistic insurance reform" at their home on Jan. 19, 2012, in Reston, Va. Quentin Tidd, 5, suffers from autism. (Jahi Chikwendiu/The Washington Post)

The Senate unanimously passed the bill Monday. The bill has already overwhelmingly passed the House of Delegates. It will now head to Gov. Robert F. McDonnell (R) for his signature.

McDonnell already 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.

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.