"One f---cking mistake and I'm going to get a stick down your throat," the man, who is not named to protect his son's identity, yelled during a 23-minute phone call.

On Tuesday, the ACT Magistrates Court heard the father was supposedly attempting to motivate the child to improve his school grades during the expletive-laden rant on November 3, 2022.

That attempt involved telling the boy he would kill him numerous times and even encouraging his son to tell his teachers about the threats to gain extensions on school assignments.

"You're not stronger than me. And even if you were stronger than me, you do not know as much as I do about how to kill people," the man told his son.

The father previously admitted to using a carriage service to menace but his lawyer told the court the bizarre and protracted outburst was entirely out of character.

"He admits he went well and truly overboard," defence barrister James Maher said.

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"He lost control and said things no child should hear."

Some of those things included calling his son a "f---ing c--- ... shit for brains" who only cares about money, does not make any effort at school, and deserves to be homeless.

"You better f---ing pass this year, or I'm telling you what? I'm going to f---ing hit you like you've never been hit before," the father said.

"Watch what happens when I'm angry. I will knock your f---ing head off."

That evening, the boy and his mother reported the conversation to police. The father told officers the abuse was "mainly out of my desire for him to learn and to grow".

Mr Maher told the court his client came from a strict upbringing, had hard work "drilled into him" at school, and faced corporal punishment as a child.

The court heard the man worked in a senior IT role "contracted primarily to the Department of Defence" and that his security clearance may be jeopardised by a conviction.

The father and his employers won't have to concern themselves with that possibility after he received a non-conviction order, and what is the Commonwealth equivalent of an 18-month good behaviour order.

The man agreed to pay $2000 if he breached his release order.

Prosecutor Hannah Lee said the phone call was not trivial.

"That's significant for a child to hear, particularly from their own parent," Ms Lee said.

Special magistrate Sean Richter told the man he had "lost it" but found the father had no intention of carrying out the verbal threats.

"You said incredibly harsh, unreasonable and offensive things to your 14-year-old son," he said.