The teenage ringleader of a prank that killed a school bus driver will serve six months of house arrest.

Robert Stanley, 75, was killed on June 1, 2002, when a boulder the size of a basketball was dropped from a bridge over Edmonton's Whitemud Freeway.

The rock crashed through Stanley's school bus windshield, striking him in the chest.

On Thursday, Judge Danielle Dalton called the incident "adolescent stupidity at its zenith."

The teenager kept a vow of silence for three years, but came forward after the wrong person was charged in the case. In March, he pleaded guilty to manslaughter.

Although he's now 19, the teen cannot be identified because he was only 15 at the time of the incident.

Dalton gave him a sentence of six months of house arrest and 18 months probation. She also sentenced him to 240 hours of community service work, stipulating that the victim's family should have input on the kind of work he performs.

'He'll never be forgiven' 

The Crown had asked for up to two years in custody, but Stanley's family didn't want to see the teenager spend time behind bars.

"He'll never be forgiven. However, we're for the idea of some sort of rehabilitation and that's what we're giving him the chance to do," said son Bruce Stanley.

Judy Stanley was fighting cancer when her husband died. She says it's been hard without him.

"I learned so much from him — kindness, not to be bitter in life because it didn't get you anywhere," she said.

"He can be at peace now. He can relax."

A second teenager charged in connection with the incident has pleaded not guilty to manslaughter and will go to trial in November.