"Those numbers were exactly what I wanted, I hadn't aimed [any] lower," she laughed.

While the Canberra student tied in the top spot for the territory with fellow year 12 student Aleksandar Rapajic, she's had plenty of time to size up her competition. The pair both go to the same public school - Narrabundah College.

Their delighted principal Kerrie Grundy said it was the second year in a row the school had claimed the top two spots in the ACT.

Aleksandar described his own result as a pleasant suprise after a busy year with a very full timetable, including an exchange trip to Prague. Focusing on history and language, he took the extra step of studying the International Baccalaureate Diploma Programme (IB) alongside his ACT Senior Secondary Certificate.

"The teachers were really good, they tried to make the extra workload not so huge, [sometimes] they'd get to school at 8am to run classes," he said.

Joanne, meanwhile, took two extension courses in physics and mathematics at the Australian National University, topping the class in physics and recording her first two high distinctions at university.

Data to be released by the Board of Senior Secondary Studies on Wednesday shows Radford College students recorded the highest average ATAR for 2018 at 87.65.

Narrabundah College students came in second with a median of 84.45, just ahead of Canberra Girls Grammar School on 84.00.

The median ATAR ranking across the territory was 77.70, on par with 2017 results, and almost 80 per cent of all students recorded a tertiary entrance score above the 65-point cut-off.

But the four-digit ranking, used to gain entry to university, is just one pathway for ACT graduates.

A total of 4560 students completed their senior certificates this year, with almost 2000 awarded a vocational qualification and many others studying under the IB.

One hundred and ten students were singled out by the board for awards in the arts, academia and community service fields on Tuesday, including singer-songwriter Lucy Sugerman, a finalist on talent show The Voice in 2017.

After walking on stage with Aleksandar to claim her award, Joanne admitted she had already mentally graduated about halfway through the year.

"It was a lot of work," Aleksandar added. "But we'd often get together all of us and study."

As classmates considered trips abroad in the new year, Joanne said she would be working part-time and brushing up on programming language, ahead of plans to study computer science at the University of Canberra or Melbourne. Aleksandar intends to stay in the capital - at least for now - studying international relations at ANU.

Also among this year's graduates were the very first cohort of Year 12s at St John Paul II College.

Principal Catherine Rey, who had just celebrated the school's rather glamourous Year 12 formal, called it a very proud moment for the students, who first enrolled in 2013.

A spokesman for the ACT education directorate said a school's success was not determined simply by ATAR statistics - there were many ways to measure student progress and achievement.

"Colleges can choose to deliver courses preparing students for university, vocational or life skills pathways," he said.

"The system’s flexibility enables colleges to select subjects offered to students according to needs and interests."

As the only ACT school still in the NSW system, this year Canberra Grammar dropped again in HSC rankings.

The private school fell to 136th spot on the league table after placing 116th the year before, 98th in 2016 and 53rd in 2015.

But head of school Justin Garrick attributed the decline to a growing number of students (40 per cent) electing to study the IB rather than the HSC.