Two summers ago, I got a text out of the blue from a teacher friend asking me to meet her ‘urgently’.

It came as a surprise — I hadn’t heard from Sarah for a while and we didn’t socialise very often — but I assumed she wanted my advice on staff room politics, or to tell me about a new man. She’d always had a fairly chaotic love life.

On her arrival, I noticed she’d lost quite a lot of weight and there was a slightly manic air about her, but that wasn’t necessarily abnormal for a teacher during term-time.

Yet after her third glass of wine, she burst into floods of tears — and to my complete horror told me she’d been having an affair with a sixth-form student.

Charlotte Parker, a 32-year-old teaching assistant was barred from teaching after admitting sending lewd messages to a 14-year-old pupil, with whom she began a sexual affair when he was between 15 and 16

He was 17, she in her late 20s, and they were ‘in love’, she said, ignoring my revulsion.

She’d decided to confess to me because I’d left teaching earlier that year and she had a notion that this would somehow make me less judgmental.

Her tale was torrid: it began with gentle flirting in the classroom, progressed to chatting on email and social media, descended into a drunken snog after prom night and culminated in a weekend away in Brighton. They were now ‘seeing each other’ in secret while discussing a future together.

I was tempted to wash my hands of her there and then, I was so disgusted. My first instinct was to report her to her school’s headmaster. But, for some reason, I didn’t.

What Sarah was doing was not just immoral but illegal, too. The 17-year-old boy was above the age of sexual consent, yes, but since 2001 it’s been against the law for a teacher to engage in sexual activity with a student beneath the age of 18. It’s known as ‘abusing a position of trust’.

Until very recently it was assumed the law was designed to protect schoolgirls from the inappropriate advances of male teachers. Nowadays, it’s being used more and more to bring predatory women teachers to justice.

Figures from the Department For Education show that last year an astonishing two teachers a month were banned from the profession for having inappropriate relationships with students.

Teaching assistant Helen Turnbull (pictured), 35, was cleared last year of sleeping with her 16-year-old pupil (pictured together right), but got a four-month suspended sentence for abusing a position of trust

The statistics are not broken down into cases involving men and women. But, if they were, it might surprise people how many offenders would turn out to be women.

There was teaching assistant Helen Turnbull, 35, cleared in November last year of sleeping with her 16-year-old pupil, but publicly reviled for kissing him and sending him provocative text messages. She got a four-month suspended sentence for abusing a position of trust and was banned from working with children.

Also last year, there was Charlotte Parker, a 32-year-old teaching assistant who was barred from teaching after admitting sending thousands of lewd messages to a 14-year-old pupil, with whom she began a sexual affair when he was between 15 and 16.

Then there was teacher Yvonne Preston, a married 49-year-old who was banned from the profession for sending a pupil cards containing phrases such as ‘the thought of not seeing you, talking to you and just being with you breaks my heart’.

The authorities’ willingness to prosecute signals a big change in attitude towards the female teacher/male pupil relationship.

Just 20 years ago, a pubescent boy exploited by a female teacher might have been called a ‘lucky-so-and-so’ and his abuse jokily dismissed as a bit of fun. But recent cases prove there’s nothing to snigger about.

I think a shift in attitudes towards older women having relationships with younger men normalises it in the minds of some female teachers. But this is an extreme perversion of the cougar phenomenon, where an older woman dates a much younger man.

In the febrile atmosphere of a school, these things always get found out — as Sarah found to her cost.

She’d noticed suspicious colleagues were constantly ‘popping in’ during break-time, apparently to check up on her, and she was convinced her emails were being monitored.

Pupils were making subtle digs during lessons; some incriminating graffiti about the ‘couple’ had appeared in the boys’ toilets.

I told her she had to stop the affair, and suggested she speak to a trusted tutor from the teaching course she’d taken several years before, which she eventually did. Immediately afterwards, he did the thing I hadn’t had the courage to do and reported her to the headmaster.

The result? Quite rightly, her career was over, her professional and personal reputation in tatters. Her mum won’t speak to her and Sarah never saw the boy again. That was part of the deal — struck by her solicitor, the school and the boy’s parents — that kept her from being prosecuted. I’d say she was lucky.

So what is compelling these professional women to risk their reputations and livelihoods to have relationships with spotty, immature teenage boys?

I think a shift in attitudes towards older women having relationships with younger men normalises it in the minds of some female teachers. But this is an extreme perversion of the cougar phenomenon, where an older woman dates a much younger man.

Another frequent feature of these male student-female teacher relationships is the fulfilment of an infantile desire for adulation and power on the part of the woman. There is a neediness, and a desire to dominate a weaker partner.

Sarah, for example, told me she loved being the powerful one in the ‘relationship’ and really got a kick out of the fact this boy had a massive crush on her.

She openly admitted the admiration she got from her male students was the best part of her job. Long hours spent marking after school had eroded her social life, she said, making her dependent on the validation she received in the classroom.

Sarah’s explanations will baffle and anger the vast majority of teachers who wouldn’t dream of conducting an affair with a child.

Yet Sarah did not consider herself a predator. She had been lonely and this ‘relationship’ made her feel good, she told me. They were both fully consenting, so what was the problem?

The problem is the recent reports that have shown the devastating life-long impact of sexual abuse on children and teens, even if they thought they were consenting at the time.

'Teens are the least discreet people on the planet,' says Chloe, author of Generation Z: Their Voices, Their Lives. 'If you have an affair with a student, it’s not a question of if, but when you will get caught' (picture posed by models)

Another factor leading to the rise of inappropriate student-teacher relationships, in my view, is the ubiquity of social media, through smartphones, tablets and laptops. Before such technology existed, the only access students had to teachers beyond the weekday hours of 9am to 3.30pm was when they bumped into them shopping in the local town.

But nowadays, through Facebook, Instagram, Twitter, blogs and email, teachers upload acres of information about themselves.

Most schools have a strict policy of not allowing teachers to interact with pupils on Facebook or Twitter. But students are wildly curious about their teachers’ lives and look for their social media profiles.

Many also have access to their teachers through school email, which means that a pupil can theoretically contact a teacher at any time.

Yet school-related chat can quite quickly veer into questionable territory, particularly if one (or both) parties has had a few drinks. I’ve seen it happen frighteningly often.

Sarah admitted to me that her attraction to her student began with innocent emails about schoolwork. They became friends on Facebook. Eventually, they began emailing nightly — and the tone became sexual after she’d been out drinking.

She began to scrutinise his Facebook page and obsess when girls left messages on it.

The emailing and social media connection made her feel their contact was acceptable. As a result, she told me she ‘wasn’t doing anything wrong, because it’s not illegal’.

But there’s a vast difference between discussing an essay on Hamlet with a pupil and asking him what colour knickers you should wear, as Helen Turnbull did.

Teens are the least discreet people on the planet. If you have an affair with a student, it’s not a question of if, but when you will get caught.

In the end these are sordid stories of adult inadequacy and depravity. They represent a huge betrayal of trust. And the more women who are being prosecuted for it, the better.

All child abuse has to be viewed in the same way and treated as a crime, whether it’s committed by a pretty 24-year-old female teacher or a saggy 50-year-old man with coffee breath.

My one-time friend Sarah deserves to be judged harshly. Teachers — all teachers — know the rules.