William Anderson walked into Skerries school, on the tiny archipelago of Out Skerries in Shetland, on September 4, demanding to see the headteacher Rebekah Gibby.
He was angry after she had complained that his grandson had been seen driving a vehicle on the island's roads, even though he was underage.
The 61-year-old started shouting and swearing when he heard Mrs Gibby was on the phone, and when she came to speak to him he swore and threatened her.
Procurator Fiscal Duncan Mackenzie told Lerwick Sheriff Court: "He then spoke to the headteacher and left with a fairly unveiled threat that he would see her at home. They live near to each other.
"This stems from a incident in which the teacher had concerns about the accused's grandson driving a vehicle on the island. I think there were no criminal procedures following that."
Mr Mackenzie said Mrs Gibby was so scared by the experience that when the police turned up to speak to her she left the island straight away, leaving the school without a head teacher.
Anderson was unable to attend the court yesterday because there was no transport day from the tiny island of Out Skerries, which lies 25 miles from the town and had to plead guilty through his solicitor Kathryn Gordon.
Skerries school re-opened this week with former headteacher Sheilagh Smith replacing Mrs Gibby, who only joined the school in October last year.
She had moved to the remote island with 70 residents with her husband after teaching at Ross High School, in Tranent, East Lothian, after frequent visits to Shetland and Skerries through their love of sailing.
Shetland Islands Council is currently advertising nationally to fill the £51,000-a-year post.
Skerries is an archipelago that lies 24 miles from Shetland's capital Lerwick. It consists of two main inhabited islands – Housay and Bruray – that are linked by a road.
Islanders have spent the past decade campaigning to keep the secondary department open. It is the smallest in Scotland with just three pupils on its roll.
The council is trying to save £3 million from its education budget, and is consulting on closing nine schools in remote parts of the isles.
Skerries has successfully fought off five attempts to close the school since 2002.
Sheriff Philip Mann deferred sentence until November 28, saying he was not prepared to deal with Anderson in his absence.
Contextual targeting label: