One of the first things Jennie learnt was that it's better if she throws left-handed. Otherwise she risks startling the children. "I have to tone it down a bit," she says. "At one school a boy just went `Whoa, Miss!' when he saw how far I could throw." It sounds like a superhero concealing their powers from ordinary mortals, but in Jennie's case there is a more prosaic reason. On the whole, men can throw further than women, and Jennie was born a biological male.
Jennie is a 39-year-old primary teacher in East Anglia and became a woman, or "transitioned", eight years ago. She is confident that no one at school knows her background, and wants to keep it that way. But she recognises this involves a degree of deception. "I'm careful not to lie, but sometimes people presume things and you don't correct them," she says.
As well as hormones and breast construction surgery, Jennie has undergone surgery to soften the look of her face. The operation took 11 hours and cost Pounds 22,000 - and she had to sell her house to afford it - but was worth it. "It totally transformed my life. People just accept me as female now and that has done wonders for my self-confidence."
If anyone at her school has suspicions, she's not aware of them. "Most people are too polite to say anything," Jennie says.
It wasn't always like this, though. When Jennie told her then-head that she was planning to transition he was horrified. Despite being aware of her rights, she felt she had no choice but to leave and started supply teaching, fitting it around doctors' appointments and operations. After completing her surgeries, she felt confident enough to apply for a permanent post.
She knows there's a risk she'll be found out, but she's ready to up sticks if necessary. "It is a lovely school but you can't spend your life worrying about it. I would just move on."
At least the law is on Jennie's side. In June 2007, Brighton and Hove City Council was ordered to pay compensation of Pounds 34,765 for discrimination and victimisation of a former teacher on the grounds of gender reassignment.
The employment tribunal found that the male-to-female teacher had lost the opportunity to find work through a supply agency after the council revealed her change of gender in a reference to the agency, despite a request not to do so.
The reference called the teacher both "he or she", "him" and "her". A second request for a reference was declined and the council refused to hear the teacher's grievance over this decision.
In addition to the order to pay compensation for loss of earnings and injury to feelings, the tribunal recommended that the council provided the teacher with a non-discriminatory reference. The tribunal ordered that the teacher's identity should not be disclosed.
But legal protection is far from the only issue. Carolyn spent the first 55 years of her life living as a man when she believed she was a woman. When the dam finally broke, it was crucial for her to be open and honest. However, this came with its own problems.
After nine years as headteacher of a 1,000-pupil secondary in Lancashire, the agony over whether to transition proved too much and Carolyn, then known as Derek, had a breakdown. She wrote to governors and staff, telling them of her dilemma. "I didn't want to deceive people. I had got to the point where I wasn't ashamed, although I didn't know how to deal with it," she says.
The letter received a hostile reaction. About 30 of her staff signed a petition asking the governors not to allow her back. But the governors decided to take no action and Carolyn returned to school, albeit opting to continue in what she calls "the male role".
In her remaining seven years as head she says the issue was never raised by a parent or staff, and there were only a handful of incidents with pupils. But the pressure to transition proved too much and she retired early on health grounds in 2002 to start the process.
Now 61, she believes she could have dealt with the repercussions of staying at school, but the consequences for her staff may have been too great. "I had a right to do what I did, but I didn't have a right to impose it on other people," she says.
Shortly after leaving school, Carolyn met a former pupil at the local sixth form college, who asked why she had left. When Carolyn explained, the boy put his hand on her arm and said: "We would have looked after you, you know."
Going through the transition at school adds another set of problems entirely. Hayley, 35, finished her PGCE in 2006, but since then has been working as a science technician at a secondary school in southwest England. She has been abused in class, had two Year 11 boys follow her home and shout obscenities outside her house, been ambushed as she cycled to work and one pupil threw a bottle of bleach at her.
Hayley says she has had little support from the school and was discouraged from involving the police. "They're frightened of the reaction from parents and just want me to disappear," she says. Hayley is now signed off sick as a result of the abuse.
Jane, then known as Peter, was teaching science and maths at a girls' school in West Yorkshire when she told her head she wanted to transition. She was pressured into resigning.
"The head said she had no problem with it per se, but she felt it was impossible for me to work as Jane at that school," she says. Supply agencies promised her work but never got back to her, and eventually she went into FE, where she found attitudes more relaxed. Now 63, she had her final surgery in 2002 and retired three years later.
Robert thinks that he has been fired from four jobs as a result of transitioning from female to male. The music teacher puts it down not to prejudice, but fear of how parents will react.
Now 34, he is a peripatetic violin teacher in northeast England. His supervisor and head of service know about his background, but no one else does, and like Jennie he is prepared to move if it becomes a problem. "I've been fired from enough jobs that I know I can start again somewhere else, although I would very much like not to."
Partners of transsexuals can also face problems. Susan Conroy has been teaching maths for 30 years and this term moved to a school in Worcester after teaching at a secondary in Swindon. Ten years ago, her husband of 33 years became female.
They have stayed together, making her an object of curiosity for pupils, perhaps exacerbated by an appearance on ITV's This Morning programme last year.
Susan, 56, says she is happy to answer reasonable questions from pupils, provided it is not during class time, and is open with colleagues. "I'm not a lesbian and I don't want to be thought of as a lesbian, and since my other half is female, I'd rather people knew."
Occasionally the curiosity tips into abuse: there was the Year 11 pupil who scrawled "trannyfucker" on her classroom wall, but mostly she shrugs her shoulders. "I've had so many other things to deal with, I won't let the kids get to me."
Alison has managed to remain at the same school after transition. After 17 years as a science teacher at a London secondary school, she told her head of her intention to live as a woman. After the initial anxiety, they agreed a plan on how to handle the announcement.
They told staff in a series of meetings and letters went to parents over the Christmas holiday. By the time pupils arrived back in January, the initial flurry of interest had died down.
Alison, 54 and now assistant head, says there haven't been any issues with colleagues, at least to her face, but she doesn't underestimate what is involved. "It's harder for the people around you than it is for you," she says. "You are solving a problem - the people around you are suddenly faced with an issue they didn't know they had."
Although her background is no secret at her school, she is reluctant for too many details to be published, for fear of attracting attention.
Alison says there have been only a handful of incidents with pupils and she deals with them as she would with any show of disrespect.
"They know who I am, I've made no secret about it, they know they're being rude and they know that rudeness is not acceptable here," she says.
"It has been easier than I thought, but you can never assume that things are going to stay that way."
Some names have been changed
TRANSSEXUALISM IN NUMBERS
Data from the Amsterdam Gender Dysphoria Clinic, widely accepted as the most reliable estimate, suggests that one in 10,000 biological males and one in 30,000 biological females are transsexual, although some studies suggest the figure could be as high as one in 500.
The causes of transsexualism are unclear, although the generally held view is that it is a mismatch in a person's sex between the brain and body. This can lead to a depression known as gender dysphoria, or gender identity disorder.
Medical treatment often involves hormone replacement therapy. Transsexual people are usually required to live as their target sex for a certain period before undergoing surgery, although not all will have genital surgery.
The right of transsexual people not to be discriminated against has been enshrined in law for almost a decade.
In 1999, the Sex Discrimination (Gender Reassignment) Regulations 1999 extended the Sex Discrimination Act of 1975 to make it unlawful to discriminate on the grounds of gender reassignment in employment or vocational training. This was widened to cover the provision of goods, facilities and services in December 2007.
The Act provides protection at work for anyone who intends to undergo gender reassignment, is already undergoing it or has already undergone it.