Sixteen children and a teacher were murdered by gunman Thomas Hamilton, who opened fire on a gym class at Dunblane Primary School on March 13 1996.
The massacre in the Stirlingshire town shocked the nation and led to the UK enforcing some of the strictest firearms legislation in the world.
There are no official plans to mark the anniversary but survivors and relatives have been reflecting on the impact of the shooting on their lives and on the country as a whole.
Dr Mick North, whose five-year-old daughter Sophie was killed, said the positive legacy should not be forgotten - that people are safer from gun crime than they were 20 years ago.
He told the Radio Times: “In many respects, the day of the forthcoming anniversary won’t be especially different - any day from the last 20 years was one for memories.
“The importance of the 20th anniversary is as an occasion when others can recall and reflect on a horrific event, and also a time when those too young to remember might learn about what happened and consider its significance.”
The retired academic feels the murder of 17 innocent victims made many people feel more vulnerable than before.
He said: “Memories of Dunblane have been sustained because of the country’s response.
“Disgust that a man could arm himself and kill so many victims with a legally-owned weapon, combined with a desire to stop it happening again, translated into public campaigns and political action.
“Handguns were banned - surely a legacy worth reflecting upon two decades later?”
Former Scout leader Hamilton was 43 when he carried out the planned execution of innocents, first cutting the school’s telephone wires before making his way to the gym hall armed with four legally-held handguns and hundreds of rounds of ammunition.
Inside the gym, 28 primary one pupils were preparing for PE class as he entered and began shooting, killing 16 children and their teacher Gwen Mayor and injuring 15 others.
PE teacher Eileen Harrild and assistant Mary Blake were among those who survived.
It emerged that Hamilton felt persecuted after complaints to police about his behaviour towards the young boys who attended the youth clubs he ran.
Among those who knew Hamilton were Judy Murray and her sons Jamie and Andy - who were at the school at the time of the shooting.
The gymnasium was demolished soon after and replaced by a memorial garden. A memorial was also established at Dunblane Cemetery, where many of those killed are buried.
Alison Ross, the sister of five-year-old victim Joanna Ross, said it is hard to cope at times but she wants people to see the positive life in Dunblane today.
She told a BBC Scotland documentary airing on Wednesday: ‘’It needs to be remembered so that everyone’s aware that we are still here, we are still getting on with our lives and we didn’t just fade into the background either.
“We still had to power on and push on with our lives, and it’s important that everyone knows we’re doing it, and doing it well.”
Aimie Adam, who was five when Hamilton opened fire on her class before shooting himself, has said she will not let him ruin her life.
The 25-year-old was shot twice but survived after a teacher got her to crawl into a cupboard.
Nursing student Aimie, who still has a slight limp, said she continues to feel guilt at having escaped but she has not let Hamilton’s actions stop her getting on with her life.
She told the Scottish Sun: “He cannot ruin my life any more. I definitely haven’t let him.”
A group called the Gun Control Network was founded in the aftermath of the shootings and supported by some parents of the victims including Dr North.
The Snowdrop Petition was launched to rally support for a crackdown on handguns in the UK and, less than a year after the massacre, John Major’s government introduced legislation to ban handguns over .22 calibre.
In November 1997, the new Labour government extended the ban to cover all handguns.
Former Dunblane primary school teacher Ron Taylor said a feeling of guilt has stayed with him for not having been able to do more to save his pupils.
A box he kept containing newspaper articles and his own written account of the event remains locked, two decades on.
“It was my school, I felt violated,” he told the Daily Mirror.