SYDNEY, N.S. -- A 15-year-old Cape Breton boy has been found guilty of criminal negligence causing death after he pushed a fellow schoolmate down a snowy embankment and under the wheels of a moving bus, killing the teen instantly in front of horrified classmates.

Provincial court Judge Peter Ross dismissed the defence's assertion that the accused was acting like a typical boy his age and was engaged in ordinary horseplay at the time, saying the young man should have known his actions could have deadly consequences.

"It is not horseplay to push someone in the path of an approaching vehicle, knowing that it is approaching," he said in his 50-minute address to the court in Sydney.

"Even at 15 years of age, (he) was capable of appreciating the risk entailed. His act was highly reckless."

The teen, who can't be named under the Youth Criminal Justice Act, stared straight ahead and showed no emotion as he sat on the front bench and the judge read the verdict in the small, but packed courtroom. One family member broke down in tears before quickly leaving.

The young boy was accused of using two hands to shove 18-year-old Christopher Chafe down an embankment outside Sydney Academy last winter. Court heard the rear wheels of the bus rolled over Chafe's head and he was pronounced dead at the scene on Feb. 11, 2015.

Defence lawyer James Snow said Chafe's grisly death was the result of "momentary inadvertence," not reckless behaviour. He told the judge-only trial that there was rowdy "goofing around" among students outside the academy that day, but he said there was no evidence of fighting or aggression.

Court heard that the two boys were engaged in banter about what might happen if the young teen pushed Chafe down the snowbank, with some witnesses testifying that Chafe goaded the boy to push him.

Ross said the school's principal said she asked the boy if he pushed Chafe and he responded, "Yes, but he told me to."

Court also heard that the boy had pushed Chafe once before the final and fatal shove sent him sliding down the bank onto a slush-covered street.

Calling it an "ominous precursor," Ross said that should have given the boy a clear understanding of what might happen to Chafe if he were pushed.

"He had, with that first push, a calibration of the force which would topple (Chafe) off the snowbank. He saw, with his own eyes, where he might land," the judge read.

Ross also said the boy would have seen the bus approaching, countering a defence argument that it was reasonable to conclude the accused did not see the bus until it was too late, based on the fact that neither boy was facing the approaching vehicle.

However, the Crown argued that evidence from the majority of the witnesses showed both they and the accused knew the yellow, 11-metre bus was coming at a relatively slow speed.

Crown prosecutor Steve Melnick said outside court that the case was unusual and difficult to try because of the accused's age, conflicting testimony and the lack of similar case law. Ross had asked the Crown and defence lawyers to search for more case law on the subject to help him determine how the age of the accused should factor into his decision.

"What you're dealing with is a number of young kids witness a very traumatic event," he said. "They had to deal with their own shock issues themselves, so it was a very trying case that way."

He would not say what he would be seeking for a sentence.

Defence attorney James Snow says it was a hard decision for the young man and his family, who reacted with emotion to the judge's verdict.

"It was a tough case to try -- there were many young witnesses and that always makes it tough," he said outside court.

The boy will be sentenced on Dec. 7, when it's expected a pre-sentence report will be presented along with victim impact statements.