The decision to open the school to girls from next year created a social media storm and water-cooler conversations across the city.

It has also called into question the issue of same-sex education, and whether it has had its time in Canberra.

No new non-government schools established across the city over the past 40 years have been single-sex.

And of the five premier boys' schools in the region across that time, only two will now remain – St Edmund's College and Marist College. Marist seriously considered going co-ed in the 1990s before the archbishop intervened.

Principal Richard Sidorko said "occasionally parents ask whether we are going to open our school for girls, but there is a certain approach and focus you have to put in place to teach and bring [the] best out in boys…Our community strongly wants boys-only education where boys can flourish academically and non-academically".

Daramalan College in Dickson was formerly a boys' school which went co-ed in the senior school in 1977 before taking girls from Year 7 upwards in 1996.

Principal Rita Daniels was assistant principal during the change-over and said it had largely been a decision instigated by parents.

Now the school has 1400 students, a waiting list "and has basically never looked back…For us it was definitely the right decision," she said.

St Patrick's College in Goulburn, one of the earliest boarding schools established in Australia in 1874, amalgamated in 2000 with the Marian College for girls to become the co-ed Trinity Catholic College.

Turning its back on 126 years of single-sex Christian Brothers education was a massive cultural change.

Similarly, Canberra Grammar must now negotiate a massive cultural change in an 87-year all-boy history.

Parent reaction on Tuesday to a new co-ed age was, predictably, mixed.

Some parents of sons were concerned the school would dilute its specialised focus on their boys and felt blindsided by the announcement, which had not been the subject of open consultation at the school. These are the families which may potentially flock to secure a place at St Edmund's and Marist as a result.

Others, however, thought the introduction of girls would benefit their sons. Parents who had both boys and girls seemed happiest, suggesting the concept of a single school, with a single pick-up and drop off, outweighed philosophical debate on the merits of single-sex education for most busy professional families.

Canberra Girls Grammar School's staunch defence of an all-girls education on Tuesday, and the presence of St Clare's College and Merici College means that there will be greater options to go to an all-girls school in Canberra than an all-boys school.

The conundrum is that the pool of potential female enrolments will shrink as parents have the option to enrol their daughters at Canberra Grammar.

One of the greatest concerns for parents with girls at Canberra Girls Grammar is the potential for their daughters to be isolated from the boys' school once it goes co-ed.

Canberra Grammar principal Justin Garrick was at pains to say he hoped both schools could continue their long association and friendship. But whether that friendship will survive the boys school's complete encroachment into the girls school's business model is another question.

Radford College may also find itself less in demand given there is now a southside co-ed option in high-end independent education.

Principal Fiona Godfrey said "while it is difficult to know what, if any, impact this will have on Radford College, it does highlight the popularity of co-educational schooling".

The only thing which seems certain is that we should all be prepared for an enrolment drive and advertising onslaught as private schools look to shore up their respective intakes for next, and coming years.

With federal funding dollars increasingly hard won and the non-government sector competitive by nature, it could be a fierce contest where every single boy and girl will count.