The debate over whether single-sex or co-educational schooling is the most beneficial for young people has raged for years.

For every argument that learners in single-sex schools thrive in an atmosphere when not having to consider or impress members of the opposite sex, there is a counterpoint that single-sex education can reinforce negative gender stereotypes. Some educators believe girls suffer in classrooms where boys can dominate; others argue that this possibility is outweighed by the social benefits of attending a school that reflects a mixed society.

The fact that girls are outperforming boys in school has raised questions about how attainment might be equalised: could boys be pushed to greater academic achievement in an all-boys environment, or would their exam fates be improved by the presence of girls in school? If girls were deprived of the presence of boys in school, would they all become hockey-playing high-fliers or socially anxious women, terrified of blokes in the boardroom?

All are questions well worth asking, though definitive answers remain elusive - probably because humans, young and old, are infinitely complex. What’s good for Sally may not work for Seema and what works for Billy might be disastrous for Benedict. So far, so confusing.

Growing awareness

These questions become even more complex when you bring students who don’t identify with a binary gender into the equation.

Non-binary (those who don’t fit the male or female binary) and transgender (those whose identity and gender doesn’t correspond with their birth sex) students have become a necessary part of the debate in recent years. This isn’t because they are a new phenomenon that started around 2010, but because growing social development and awareness around the issue means that trans and non-binary kids must be considered when weighing up the pros and cons of single-sex education.

How does a single-sex school practically and ethically deal with a child who wants to transition to the other sex? Can a non-binary student attend a single-sex school? And do non-binary or trans kids make the whole institution of single-sex education outdated or even obsolete? These aren’t just philosophical or ethical questions, but actual dilemmas that have faced - or are currently facing - schools all over the country.

For example, I know a head at an all-girls secondary in the Home Counties who came to the difficult decision to ask a Year 11 student to leave when she began to identify as male and began the hormone treatment (the earliest you can start this is 16). He didn’t cope well with his new school environment and his parents asked if he could return to the original school. After a consultation with students and parents, it was unanimously agreed that he should be able to and he is now happily completing four A levels.

I have also heard of a similar case at an boys-only private school in London, though the student was transitioning from male to female. There was no debate or consultation with students or parents: she was asked to leave immediately. “I was made to feel like a freak and like I was breaking some sort of rule,” she tells me. “The decision I was making wasn’t like refusing to wear a tie. The school was conservative and very ‘boyish’, so they simply didn’t have the facilities to cope with my needs and there was no possibility of staying.”

She raises an interesting point. While most schools are effective in ensuring students don’t get discriminated against on the basis of gender, race, sexuality or disability, what is their responsibility to transgender students in a single-sex environment?

“Your foremost concern is for the welfare of the child. You want to support them at what is already an incredibly difficult time for them,” one head tells me. “But then you have all the other children and parents and their needs to consider. And then you have the technicality of the issue - if we have a male student in the school, can we really still advertise ourselves as an all-girls school and the benefits we believe come with that?”

Rise in trans referrals

In the UK, many single-sex schools are found in the independent fee-paying sector, but about 12 per cent of maintained schools are single sex, with 226 girls’ schools and 184 boys’ schools out of 3,400 secondary schools. In 2015, the NHS’s only facility for trans kids, the Tavistock Centre, received 1,419 referrals. Hardly the epidemic numbers some parts of the media would lead you to believe, but 10 times the total in 2010.

The best-reported recent case was at co-ed Brighton College, which reacted by announcing that it was relaxing its uniform rules to accommodate transgender pupils.

It is statistically increasingly likely that single-sex schools will have a transgender or non-binary student in their community. As such, it is of paramount importance that they have strategies in place to deal with it, if and when they do.

A teacher from South London who teaches in an all-girls grammar describes how her school “panicked” and dealt with a transitioning student badly. “We basically told the girls to hush it up and not talk about it all, in part because we didn’t know how to deal with it and also because we were genuinely worried about protecting the identity of the student,” she says.

“Of course, this made it seem like something we were ashamed of and the parents withdrew the student somewhat acrimoniously.”

There will also be those who take an even harder line. No doubt sympathetic to what is an incredibly difficult decision, I have been made aware of some who take the attitude that it is simply not possible to allow a student to remain if they no longer identify as the gender of the rest of the student body.

What is apparent is that single-sex schools seem to be making decisions about trans or non-binary kids on a case-by-case basis - and some with great success. But is this good enough?

It seems a particularly cruel fate for trans or non-binary kids to be debated over as if they were a tricky policy or law to be passed. There would rightly be an outcry if a school debated whether they could keep a student who was disabled or gay, so is it fair to do this to trans or non-binary students?

One could argue that the rise in number of trans and non-binary young people presents a strong argument against maintaining single-sex education, but interestingly, the pupil mentioned earlier who has returned to his all-girls school, remains adamantly in favour of the system. “I loved the girls-only environment, loved my school and I really think girls in particular learn better in a single-sex environment,” he says. “Despite my situation, I think it’s the type of school everyone should go to if they want to.”

Chloe Combi is a former English teacher and author of Generation Z: their voices, their lives, published by Random House. Her second book is due to be published this year