BOSTON -- When does spanking a child turn from old-fashioned discipline into child abuse?

The state Supreme Judicial Court confronted that question Monday, hearing the case of a Woburn minister who was investigated by state child welfare officials for spanking his son.

Juliana Rice, the assistant attorney general who represented the Department of Social Services, acknowledged that spanking, in itself, isn't illegal.

She said the DSS filed a report on Donald Cobble after determining that the spanking in his case raised a "substantial risk of physical injury" to his son.

She said that determining that there was a risk of physical injury was one of the "delicate judgments that have to be made" by the DSS's professional social workers.

Cobble's attorney, Chester Darling, disputed whether there was a risk of injury in Cobble's spanking his son, Judah, who is now 12 years old.

"Every scrap that's in that record supports the fact there was no injury to this child," Darling told the court.

Cobble spanked his son, both sides agreed, once to twice a month, using the end of a leather belt. The spankings, given while the boy was fully clothed, left red marks that disappeared within hours.

Darling called it "mild, loving, routine, structured" spanking and he argued that spanking is a parent's own business -- except in cases that could be addressed by the criminal law.

"All of us have seen terrible, egregious cases. ... The penal statutes adequately address that," he said.

Both Darling and Rice were bombarded with an unusual amount of questions by the court.

Rice was questioned particularly closely about whether the DSS had any guidance it could set out for parents.

"You have no way of giving guidance to parents as to whether or not a report of physical abuse will or will not be substantiated," said Justice Margaret Marshall, who has been nominated to be chief justice.

Marshall focused on the fact that the department had only determined there was a "risk of abuse" in Cobble's case, not actual physical abuse.

Justice Roderick Ireland asked how a parent could know when their behavior is unacceptable, noting that parents might be looking to the court's opinion for guidance.

Rice said the department wasn't banning physical punishment. She wouldn't offer examples of acceptable punishment, but she said Cobble's specific actions weren't acceptable.

"It's not the department's role to prescribe physical or any other punishment. ... These particular facts and circumstances represented a risk of abuse," she said.

The court took the case under advisement.

DSS filed abuse charges against Cobble but offered to drop the charges if Cobble agreed to stop spanking. He refused. DSS has taken no further action against him.

Cobble, a pastor at the Christian Teaching and Worship Center in Woburn, has quoted Biblical passages to explain why he spanks and has argued that state is interfering with his religion if it interferes with his spanking.

But the SJC justices largely passed that argument by on Monday.

Cobble, a pastor at the Christian Teaching and Worship Center in Woburn, said after the hearing: "I see that it was made clear that the DSS has a problem here. They say, 'We permit spanking.' But then, they're really saying, 'We don't permit spanking."'

"I'm saying, they're anti-spanking," he said. "Most people I talk to think it's illegal to spank in this state, but that is not true."