It comes as the year 12 students discovered the ACT Scaling Test, which is required to get an ATAR for university entry, has been delayed to mid-October.

The Parents and Citizens Associations of Lake Ginninderra and Narrabundah Colleges wrote to the ACT education and health ministers on August 1 foreshadowing a lockdown and pleading for the senior students and college staff to be vaccinated.

President of Lake Ginniderra P&C Ben Vagnarelli said the parents would like the ACT to follow the NSW model of trying to vaccinate the year 12 students from in high-risk areas of Sydney quickly.

"The Delta strain has obviously changed things so much and so the families with students of the college have told me they'd like to see the vaccine rollout reconsidered," he said.

ACT Chief Minister Andrew Barr told a media conference Pfizer vaccines appointments, the recommended vaccine for 16- to 39-year-olds, were unavailable until the end of October and so year 11 or 12 students would need to wait until more supply came through.

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The Board of Senior Secondary Studies announced the ACT Scaling Test (AST) would be postponed from August 31 and September 1 until October 12 and 13 because of the lockdown.

"The board acknowledges that this can be a stressful time for students and families," board chair Roberta McRae said in a statement.

"The board is committed to the health and wellbeing of students and to processes that support the validity of academic results.

"All plans and arrangements for the AST will be subject to the public health directions and advice at the time."

The decision reduced the anxieties of year 12 students who had been waiting for information on the AST since the lockdown extension was announced.

University of Canberra Senior Secondary College Lake Ginninderra student Ellen Johnson said she was glad it was going ahead but it was a bit frustrating the test would now be closer to the end of the year.

"It's a bit nerve-wracking, I guess. So it's a kind of added stress for a bit longer, as well," she said.

She said uncertainty remained over whether this year's cohort of school-leavers would have special consideration to get into university when their college time had been interrupted with two lockdowns.

Melba Copland Senior Secondary School student Lily Kelly-Clark, who is aiming to study engineering at UNSW, was relieved the test would not be crammed into the final weeks of term 3.

"I'll probably keep up the same prep to be very, very prepared for the test but it takes a lot of the anxiety out of it," she said.

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