Watching herself on video, Sally Tate shudders to see the tense figure who with shoulders hunched and in a desperate voice struggles to get pupils' attention.
"It's just so insidious," the 46-year-old physics teacher said. "It gets inside you. You think that, because you're having trouble with some of your classes, you're just not good enough."
Earlier this term, Ms Tate allowed BBC cameras into two lessons for a series on confidence in the workplace. They filmed her struggling to control 14 and 16-year-olds and forced her to watch her own classroom techniques.
"Students were mucking around with equipment. There was always someone being uncooperative, or even defiant. And I was working too hard, trying to prove that I was good enough. I felt I was the weakest link in my department."
After three years of struggling with pupils at River Leen comprehensive, in Nottingham, one of the lowest-performing schools in the country, Ms Tate found her confidence shattered.
Her frustration in the classroom took its toll socially. She began to question her worth and had difficulty in making friends. And her lack of success at work made it hard to relate to her two teenage children.
When the BBC offered to give her a "confidence makeover" for its new series, Ms Tate agreed immediately. She was taken for a day-long session with Ros Taylor, a psychologist.
This involved counselling, psychological exercises and role-play as well as an analysis of Ms Tate's classroom technique. She was also offered advice on dealing with pupils who misbehave.
"I was told to talk about positives, and give positive feedback. Now I don't shout at pupils. I wait for them to be quiet and say, well done.
Because my attention isn't focused on getting them to behave, I find I can do more with them."
Previously, when pupils disrupted the class, Ms Tate felt personally responsible. Now, she passes blame on to the pupils. Ultimately, she says, they choose how to behave. But they also respond to expectations. She now walks into a classroom anticipating good behaviour: "Pupils know when I mean business, and I won't brook any interference. It makes a real difference to our relationship. The nonsense stops."
The change has been obvious. Ms Tate's Year 9 class now willingly sits down and writes an essay in her lessons. She has also learnt to relax in class.
Where previously she might panic if her lesson plan was not immediately to hand, she now feels able to pause at the start of the lesson, and ensure that she is organised before proceeding. "As a teacher, I was used to looking at my mistakes. Now I look at my achievements. If one lesson goes well, I go into the next feeling much more confident. I don't feel inferior to other teachers. I just feel better in myself."
Confidence Zone, is on BBC2 on December 1
How to let go of the panic
* Judge yourself by your achievements, not your mistakes
* Ensure that your body language reflects self-assurance
* Remember that pupils, not teachers, are responsible for misbehaviour
* Emphasise the positive, congratulating pupils for good behaviour
* Allow yourself to pause and get organised before beginning a lesson
* Expect pupils to do what you say, rather than worrying that they will ignore requests
* Believe that you are good enough, rather than struggling to prove yourself