One of Sydney Diocese's oldest ministries is breaking its 122-year-old tradition as an all boys institution by going completely co-ed, but in a radically different way.

Backed by the latest scientific research, St Andrew’s Cathedral School is set to run parallel single-sex classes for middle school students.

This revolutionary educational strategy is called ‘twinning’ and it allows St Andrew's to grow its Christian ministry while retaining its current strengths in boy's education.

Head of School, Phillip Heath, says the latest neurological research is highlighting differing maturation rates between girls and boys during adolescence.

“Research in the area of the physiology of the male and female brain has concluded that boys and girls mature at different rates. This has enormous implications for educators,” he says.

Twinning is a relatively new educational system.

A number of leading independent schools in Victoria as well as schools in the UK and US have introduced similar models with great success, says Mr Heath.

"We have taken the learnings from these schools," he says.

At St Andrew's it will see the core subjects of science, maths and English taught in a single-sex environment.

While the same curriculum will be taught to both girls and boys, the teaching styles and resources used will be modified to suit specific gender learning needs.

Boost for Christian ministry

Mr Heath says one key reason St Andrew's is moving co-ed is to help boost Christian education.

He says the school has been surprised at the difference in biblical knowledge between the boys who have been educated at St Andrew's and the girls who come into the school in Year 10 for the co-ed Senior College.

"We are finding that the girls who come into our Senior College have a very limited understanding of the Scriptures," he says.

"By going co-ed we increase the number of people who have an opportunity to hear the gospel."

A high proportion of St Andrew's families say they have "no religion'.

Almost half of the student body identify as Anglican, but only one in four attend church regularly.

The co-ed plan will also help St Andrew's better serve clergy families, which Mr Heath says is a core goal of the school.

Overall the plan will see primary school students taught in mixed gender classes, with the addition of two more primary classes next year.

At least one additional class per grade will be added to the middle school.

With the school taking over an additional level of St Andrew's House, Mr Heath says they can cater for the growth within their current space. 

The co-educational Senior College launched in 1999, is now at full capacity and will continue its current operation.