The depute headteacher at a primary school in Glasgow was acquitted on August 29 of assaulting a pupil. The boy had previously been suspended six times, once for attacking Mr Simpson.
"It was always at the back of my mind, until I stood up and the sheriff said 'Not guilty', that should this person prevail, I could lose my job.
Not only your job; your career and your whole life would change completely."
His biggest anxiety was that people might doubt his innocence.
"The turning point for me was when I went to court. The sheriff said: 'In every particular case I find in favour of the defence.'
"That a child who is known not to be always truthful can make this up and disrupt the school is disturbing.
"It's about nobody taking the responsibility to make a difficult decision.
The whole thing was unnecessary."
He is still "very bitter" about the police investigation and feels similar matters should be referred to a senior officer.
"In general, schools present a positive image of the police. It becomes difficult to sustain support for the police when this happens.
"When 90 per cent of cases like this are thrown out, it's fairly disturbing."
Mr Simpson kept his suspension and the court case a secret from his children, leaving the house before they came home, to pretend he was at work. "One's almost 9, the other had just turned 5. You can't involve them in this. They understand the police take away bad people who do wrong things, not the people whom others have concocted stories about."
He is grateful for the stupport he was given by the school. "Staff organised a number of nights out to rally round. At least one of them phoned me every night. A number of people at authority level were very supportive."
However, he appreciates that not all teachers who find themselves in a similar situation have such a strong support network. "There needs to be another agency which supports you in that situation," he says. "You're very much in the dark.
"You have a situation where a professionally qualified person can lose their career over an attempt to do the right thing. All the work that you put in could be destroyed on a genuinely made decision in that split second when you decide 'Do I intervene or do I let this blow up into something that could turn into violence?' Thankfully, for the sake of all our children, most teachers would still intervene in this type of situation."
He believes training for all teachers, with enhanced training for pastoral staff and senior management, would be a positive, practical step.
"All education authorities have a duty of care to clarify, for their staff, appropriate methods of restraint and the situations where that would be deemed totally acceptable and when it would be considered questionable," he says.
"We need a clear statement from the Scottish Executive about when it is appropriate to intervene.
"There also needs to be a recognition that some communities are particularly violent. That kind of violence comes through to the educational environment.
"When boundaries are not enforced in the home, it makes it very difficult in the classroom.
"There are few other forums where someone can attempt to assault people and then bring charges against them. It seems that any child who wants to can accuse a teacher of anything. The situation becomes unworkable.
"Other public institutions wouldn't tolerate this - if a child threatened a police officer, for example.
"I'm over it; I'm reasonably resilient. But I don't want any other teacher to have to go through what I have."