It was just after registration on a grey morning at Pantglas Junior School and school children were sat at their desks.
But moments later, as Hettie Williams was teaching her first-year class, tragedy struck when a coal tip slid down the mountainside, engulfing the village of Aberfan.
The 23-year-old made her terrified pupils hide under their desks as the walls cracked around them and would later lead them to safety trying to shield them from the horror which surrounded them.
But 109 children at the school, along with five teachers, were among those who would not survive the tragedy on 21 October 1966.
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Ms Williams died on August 3 this year of a heart attack, aged 75, and her pupils flocked to her 500-strong funeral to remember her actions on that horrific day and say “thank you and goodbye”.
Ian Davies was just seven-years-old when there was a “loud roar” as the avalanche hit the school while he was sitting in her class.
“Hettie looked after us that day but more than that, she was so impressive in the weeks and months that followed,” he said.
“She was a constant, trying to keep things normal, and it took me a long time to realise how hard that must have been for her.
“I’m so appreciative, and that’s why I needed to be at her funeral – to say thank-you and goodbye.”
At just 23, and known by her maiden name Miss Taylor, from Rhymney, Caerphilly, she had only been teaching at Pantglas for a few years when the landslide happened.
But Mr Davies, who is now a health and safety manager based in Merthyr Tydfil, said she remained calm and measured as she tried to help the children.
“We had only just had registration and there was an enormous loud roar I can only liken to a jet engine,” he said.
“Hettie instructed us to get under our desks. She was so calm and measured. She tried to open the door but there was a lot of rubble in the way.
“Eventually the caretaker came and freed us – he himself lost two sons that day.
“Hettie took us out into the yard and told us to head for home.
“We still had no idea what had occurred; she told us to run and not look back.
“What she did the rest of the day, I have no idea, but I’m sure it wasn’t very pleasant.”
As impressive as Ms Williams’s actions were that day, Ian, 59, said he was more impressed by her actions following the disaster.
He said: “When the school reconvened several weeks later in a local working man’s club, she was there. A lot of people would never have been able to return to work.
“They would have needed counselling or medication.
“So it was a massive boost for the class to have a familiar face there.
“It was incredible.”
Another pupil David Davies, 60, who was taught by Ms Williams the year prior to the disaster, said: “I always remember her as an inspirational teacher but more so as a wonderful human being.”
David, who survived after being buried under the rubble and suffering severe head injuries, said all the teachers were heroes that day in their own way.
“Certainly as a young teacher, it was quite a feat to keep calm a class of seven-year-olds and get them out safely amidst the chaos.
“Hettie also had to identify my own class teacher, Michael Davies, 21, who didn’t survive.
“They were friends so she knew what he was wearing.”
Mr Davies, a retired solicitor and chairman of the Aberfan Memorial Charity, said Ms Williams never forgot the events of that day.
He said: “Every year, Hettie came to lay flowers on behalf of all the teachers in the memorial garden.
“But she said she had never been able to face going to the Aberfan Cemetery memorial as that would have been too painful and difficult for her.”
Hettie went on to have a long teaching career, first back at Aberfan and then at various schools across Caerphilly county.
She married her husband Ralph, had a family and was due to celebrate her fiftieth wedding anniversary.
David, who also attended Hettie’s funeral at St David’s Church in Rhymney, said: “I think the 500-strong congregation shows the level of respect people had for her.
“It was an incredibly moving occasion, and a fitting send off for a special lady.
“The people of Aberfan will never forget our dear Hettie.”