She was three years into her training to be a nurse when she badly injured her back, putting an end to hopes of a career in patient care. Lying in the Western General Hospital in Edinburgh, she took only five minutes to decide what her subsequent career path should be.
"It was not a very considered decision to go into teaching, but it was a good decision," says Mrs Clark, whose special school received an unprecedented 10 "excellent" grades and six "very goods" from the inspectors.
This puts Clippens ahead even of St Andrew's Secondary in Glasgow, whose HMIE report hogged the headlines elsewhere last week.
The report described Mrs Clark as "an inspirational leader", but she goes back to her early days in teaching, at Kinneil Primary in Bo'ness, to find the school leader who inspired her.
Alan Macdonald, then depute head at Kinneil and only recently retired, was, she says "light years ahead of his time".
She recalls: "He was into active learning, giving children responsibility for their learning, seeing teachers as facilitators, and things being purposeful and fun. I just sucked it up like a sponge in the time I was there."
It was Mr Macdonald, she says, who taught her the basic principles of self-evaluation - to ask the question: "why is that child not learning or bored?"
Very quickly, she decided she wanted to specialise in working with children with additional support needs, so she moved to Broxburn Primary's special unit for children with moderate and severe educational needs.
The impetus was her drive to find out why some children don't learn, which had been sparked at Kinneil. She had discovered there that the real prize in teaching was getting it right for all the children.
"I had a number of children for whom we were not getting it right, and I found myself spending a disproportionate amount of time thinking about them. When I saw bits and pieces of success, I realised that was what I wanted to focus on."
In 1987 she joined Clippens as assistant headteacher, becoming head two years later. The school has a roll of 58 pupils aged from five to 18 with complex learning difficulties, sensory impairments and physical disabilities. Its Lismore Unit provides support for autistic pupils.
In what was, by any standards, an outstanding report, HMIE gave particular praise to the school's creative teaching approaches, its self-evaluation, the quality of its curriculum, and its achievements in communication and language.
Mrs Clark's search for best practice across the UK and beyond was also recognised, along with her support for staff's continuing professional development.
If "self-evaluation" may seem like something of an HMIE mantra, Mrs Clark sees it as something Clippens was doing well before it entered the general vocabulary.
"Our job is to educate as well as we can the group of pupils for whom we have responsibility, each and every one of them. That requires us to be skilled in a range of things and key to that is the skill of differentiation," she says.
That is something many mainstream teachers may not have had the opportunity to develop. "Any time class teachers are with us from mainstream schools, what they tune into very quickly is the highly skilled level at which our teachers operate," she says.
Recently, two of Clippens's pupils learned how to tell the time. For staff, that was akin to secondary pupils achieving five As in their Highers - and it was celebrated as such.
The aspects of the HMIE report that gave her the greatest pleasure were the recognition of the staff's effective teaching and learning. That recognition included Clippens's search beyond the elaborated 5-14 curriculum, which she felt did not provide sufficiently for her pupils'
needs, to the Equals curriculum in England.
Clippens has adopted the work of Flo Longhorn on early sensory learning, Les Staves's work on mathematics for children with additional support needs, and Veronica Sherbourne's developmental movement programme for PE based on shared communication.
"A lot of good teaching is good teaching wherever it takes place, whether it is Higher physics over there, or teaching children to walk along the pavement safely here," says Mrs Clark. "We have invested a lot of time in staff training," she explains.
Mrs Clark sees the role of headteacher as a facilitator - "someone who empowers other people to want to be the best that they can be, whether they are children or staff."