When Jenny Tiffen heard that St Clare's College could become coeducational, she thought it was a badly timed April Fools' joke.
It was only when she read the letter from principal Dr Ann Cleary that she believed the news.
The school community has been reeling since the Catholic Archdiocese of Canberra and Goulburn Education Limited put forward a plan to change the all-girls school into a coeducational school to meet demand in the south of Canberra.
The Catholic Education system is also exploring expanding or repurposing existing school sites in the south-west of the ACT or acquiring land in NSW to meet demand.
Mrs Tiffen had one daughter graduate from St Clare's and has two daughters at the school, while her son attends St Edmund's College across the road.
She said she would probably move her daughters to Canberra Girls Grammar School if the plan to bring boys to St Clare's College went ahead.
"I think at the moment one of the reasons why I love St Clare's is that the captains are girls, the STEM leaders are girls... the [students] that are on the debating team are girls ... because they're not having to compete with boys for those positions there's just more opportunities for girls at the all-girls school."
St Clare's College community council chair Dr John Norgrove said the majority of the feedback he has received does not support the idea of the school moving to a coeducational model.
"Among the options in the plan the one proposing a co-educational model at St Clare's has upset the community the most," Dr Norgrove said.
"Several families have informed me that they would leave St Clare's if it was to go co-ed. I'm informed that families considering sending their daughters to St Clare's in 2028 are reconsidering their decision to do so given the current uncertainty, and the co-ed proposal in particular."
But families wishing to move to another girls-only high school may be left with limited options.
The only other Catholic system girls high school, Merici College, is approaching capacity with 1039 students enrolled this year.
Some parents could be priced out of Canberra Girls Grammar School, an Anglican girls school with fees reaching about $35,000 a year for year 12 students.
There are two independent Catholic boys schools in Canberra's south that do not fall under the Catholic system: Marist College Canberra and St Edmund's College.
The archdiocese has plans to expand the number of enrolments across systemic schools from 24,000 to 30,000 by 2033.
It has identified Batehaven, Yass, Goulburn and Queanbeyan as areas of growth.
A survey of Catholic school parents with children in kindergarten to year 5 in the ACT, Queanbeyan and Yass showed a strong demand for a new co-educational secondary school on the south side of Canberra.
St Mary MacKillop College - the only coeducational Catholic high school in the south - knocked back more than 150 families wanting to enrol their children in year 7 in 2027.
St Clare's College enrolments are 20 per cent down over five years, from 1087 students in 2022 to 872 at the beginning of 2026.
In a letter to Dr Cleary, Catholic Education executive director David de Carvalho said the proposal to enrol boys at St Clare's was "not related to any concern about the quality of education, leadership or quality at the school".
"The reaction from the St Clare's College community is understandable," Mr de Carvalho told The Canberra Times.
"I'm aware that even raising this possibility is contentious because St Clare's is a strong and much-loved Catholic school with a proud history and an excellent reputation."
While many parents believe a single-sex education will deliver better academic results, the research is not conclusive.
Dr Laura Scholes is a professor at the Australian Catholic University Institute for Learning Sciences and Teacher Education and leads a program of research on gender and literacy in the digital age.
She said there was nothing conclusive in the academic research to show that single-sex schools were better for academic achievement.
"It's dependent on the school, and boys still make a modest improvement in maths in single-sex schools, and there's little difference in the girls' outcomes," Dr Scholes said.
"I think some of the the reasoning is about the STEM subjects for girls because people feel that they'll have more time and attention in the classroom and become more confident in those STEM subjects that traditionally they haven't been entering."
A 2023 report commissioned by Catholic Schools NSW analysed the average NAPLAN scores of coeducational and single-sex schools. It found after accounting for socioeducational background, single-sex schools tended to have slightly higher NAPLAN scores than coeducational schools, although with wide variation among individual schools.
It also found that boys in single-sex schools performed better than expected in numeracy but there was little gain for girls in reading.
Dr Scholes said often single-sex schools - mostly boys schools - became coeducational in response to financial crises.
"But also this generation of parents have different ideas about the social context that they want their children in, which the co-ed [model] is much more like real life.
"And there's some studies showing that it takes young people some time to transition when they're in real life with mixed sexes. And there's also I guess all that negative publicity about the all-boys schools with hyper-masculinity."
The changes to make St Clare's College suitable for boys and girls go beyond adding boys' toilets and change rooms.
Single-sex schools gear their whole offering around catering to either boys or girls. This affects the kinds of texts read in English and the extracurricular offerings.
Dr Norgrove said there would be a significant cultural change at St Clare's if coeducation was introduced.
"The College promotes female leadership and personal development and provides a place for girls who choose to learn surrounded by other girls.
"The many benefits of an all-girls College would be removed from the girls and families who have chosen St Clare's. Girls lose out if St Clare's goes co-ed."
While St Edmund's College is operated by Edmund Rice Education, the boys share some extracurricular activities with the St Clare's girls.
Mr de Carvalho said the archdiocese was "actively exploring" two other options: redeveloping existing sites or finding new land in NSW.
The archdiocese could look to several of its ageing sites in Canberra's south to meet the demand for a high school.
One option could be the St Peter Chanel's Church site in Yarralumla, which had a primary school until 1989. The church hosts only two Masses a week but has a well-used hall, an oval and St Vincent de Paul located in offices on site.
Some of the existing southside schools, such as St Benedict's Primary in Narrabundah, St John Vianney's Primary in Warramanga and St Jude's Primary in Holder could also be ripe for redevelopment.
An ACT government spokesperson said three sites would be released for non-government schools over the next few years.
These include the Stromlo Reach estate in Denman Prospect, Kenny in east Gungahlin and Molonglo Valley stage 3 east. These land releases will probably attract expressions of interest from many non-government school organisations.
Over the border, the Googong and South Jerrabomberra developments continue to take shape, but it is unclear whether land for a non-government school will be made available.
Mrs Tiffen was part of the fight to keep St Bede's Primary School in Red Hill open in 2021. She hopes this time the community response is taken into account to keep St Clare's College as a girls-only school.
"I think Catholic Education just wants more places under their own umbrella, and so I think they should definitely be looking at the new land release... rather than close an option that's already working really well for the girls' school."
