It was July 2017 and, with more than four years’ experience as a qualified primary teacher behind her, Megan Taylor was doing well. She had been promoted to a leadership post at her school, in the south-east of England. She was doing so well, in fact, that she was approached by another school about a new job. And that conversation led to a question: what was she paid?

“To my shame, I didn’t know what pay scale I was on,” she says. A discussion with the school business manager revealed she was on just £28,700 a year – and that wasn’t all.

Taylor – not her real name – had a male opposite number with whom she worked closely. They had similar experience and qualifications; they each did a very similar job. Although she had been at the school since qualifying, he had been headhunted in 2016. She decided to ask him what he was being paid.

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“I went into his room and said: ‘What pay scale are you on?’ He said: ‘I’m on M6’ – that’s the top of the pay scale. I was on M3 – that’s a £7,000 difference.”

Taylor calculated her colleague was earning about £35,600. He told her he had jumped pay scales when he took the job.

Taylor is calm and direct as she tells her story. But as she recalls that conversation, the emotion breaks through. “I was just filled with this … anger, and shock,” she says. “Oh my goodness – I felt I’d been completely used and taken for a ride.”

Taylor is keen to speak out by talking to the Guardian. We have to conceal her identity, however, to protect that of her male colleague, who is still in his job.

Taylor’s experience, it seems, is all too common. And with the gender pay gap high on the news agenda, women in education are becoming increasingly vocal on the subject. In less than three years, the WomenEd group, which campaigns on the issue, has garnered more than 17,000 followers on Twitter and is becoming a serious force. Vivienne Porritt, a former secondary head and a government adviser, and one of the group’s co-founders, says: “We’ve talked to 4,500 women teachers and leaders in the last three years, and just a handful knew they could argue for more pay. As a headteacher, it never occurred to me to ask about my pay, I was just grateful they were giving me a headship.”

But, Porritt adds, that isn’t the whole story: “It isn’t only that women don’t ask – men are offered more, or there’s an assumption they will want more and so there’s a conversation about that.”

Official statistics bear out the feeling that the gender pay gap is as live an issue in schools as it is elsewhere. Government figures show that although young female teachers earn slightly more than male colleagues, they slip back as their careers progress. A woman under 25 in a local authority secondary school, for instance, might on average expect to earn £24,500 – £500 more than a male colleague. But by age 55-59 she would find herself on £44,700, while a man would earn £47,900.

Although two-thirds of secondary teachers are women, fewer than four out of 10 secondary heads are female. In primaries, one classroom teacher in seven is male, but more than a quarter of heads are men.

The reasons for this are complex – women are more likely to take career breaks; they are more likely to go into part-time roles where promotion is less likely.

But those aren’t the only reasons why women earn less in schools. As Taylor’s case demonstrates, women are often held back by a culture in which jobs are offered through personal connections and in which if you don’t ask, you don’t get.

Natalie – who wants to remain anonymous – is a secondary teacher in the south-west of England. After 15 years she applied for and got a position as deputy principal, only to learn a few weeks later that a male colleague in a sister school, where she had until recently been a member of the leadership team, had been promoted to the same role without any formal process.

“No advert, no application, no presentation, no interview. I was furious,” she says. “I honestly think he just went and asked for the job.

“There were three other people who I know for a fact would have gone for that job if it had been advertised.”

When schools compete with each other for staff, and when posts are often filled without advertisement, then those who are less forceful in their demands can lose out.

There’s a belief, too, that academisation has played its part in deepening this gender divide. And there are figures that back up this view. Government statistics show female teachers in local authority primary schools earn on average £1,800 a year less than male colleagues, while those in primary academies earn £2,800 less. In local authority secondaries the gender gap is £2,600; in secondary academies it is £3,000.

Under new legislation, organisations with more than 250 employees must report their gender gap for mean hourly pay by April this year. An analysis by the Guardian of the first 1,000 to report included 40 academy trusts – and their pay gap was much higher than average. While the average gap between men and women was 11.8%, academy trusts had an average pay gap of 19.5%. Experts say this is not surprising, as schools have large low-paid workforces of classroom assistants, lunchtime supervisors and cleaners, which are largely female.

Kay Fuller, an associate professor at the University of Nottingham, has been interviewing WomenEd members for a research project. “There are also issues regarding the fragmentation of the education system,” she says. “Local authority links have been broken. If it is difficult to recruit staff or leaders to a school there is much more flexibility to decide pay awards. There are market forces. Traditionally there was space in that relationship for monitoring equal opportunities – who monitors these things now?”

Some female teachers feel directly discriminated against on pay. An assistant principal in a secondary school – who wanted to remain anonymous – told the Guardian she felt her career stalled after she had a baby and asked to work four days a week.

She was one of four in her role at the school. Within a year of her return from maternity leave, the other three had been promoted to senior assistant principal and given a pay rise. “I was furious,” she says. “Everyone who was promoted around me was male or childless. I had excellent results, far better than those who were offered more money. So I looked for another job and left. Two other assistant principals who had maternity leave before me also left within a year or so of returning to work, so it felt like a pattern to me.”

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The Home Office, which is responsible for government policy on women and equality, said in a statement that female classroom teachers – those who have remained in the classroom and not been promoted, as opposed to all female teachers – earned more on average than men in the same position. This is likely to be because a greater proportion of men are promoted out of those posts.

“While acknowledging that there is always more to be done, the gender pay gap in teaching appears to be narrowing,” it said.

Taylor’s former employer told the Guardian it had struggled to recruit into the male teacher’s role and that while it recognised there was a pay differential, this was due to material reasons that were not related to gender.

“I kick myself for not asking for a pay rise,” says Taylor. “I thought I just wasn’t good enough. I thought: ‘When they think I’m good enough, they’ll give me more.’ If only I’d had the guts to ask – it’s your right to question your pay. I didn’t think I could.”