Figures from the ACT Board of Senior Secondary Studies show schools reported 245 cases of academic dishonesty by years 11 and 12 students last year, up from 178 in 2012.

Principal associations have described no change in plagiarism detection policies across the period, but said longer-term trends of better online checking skills of teachers and heightened pressure on students may have played a part.

ACT Principals Association co-president Michael Hall, principal of Erindale College in Tuggeranong, said the internet was both a temptation for students and a tool teachers could use to track cheating.

"Teachers get much, much better at analysing pieces of work," he said.

"As the web has been proven to be more accessible to a greater range of students, and the pressures on students grow, the complicated lives – balancing the social, the work – it's easier to put an assessment in that's off the web."

Mr Hall said minor cases of dishonesty would not be forwarded to the board.

"Those 245 cases, you would find there is serious misconduct that would move the principal to say this has had a significant enough effect on the result of the student to warrant it being reported," he said.

Student numbers in the final two years of schooling have shifted little over the period, with 10,140 year 11 and 12s last year, up 1.7 per cent - or 171 students - from 2012.

Board director John Stenhouse said the cases were a tiny proportion - less than 0.1 per cent - of the 360,000-plus internal assessment tasks the senior students did each year.

"Another way of looking at this is that on average over the past three years about 1 in every 1600 items is a case of academic dishonesty," he said.

Association of Independent Schools of the ACT executive director Andrew Wrigley said teachers deserved credit for what may have been improved efforts to track unoriginal work.

"I'm suggesting there is another way of looking at [the figures], we should applaud the teachers in all of the schools, and collectively they may be getting smarter in their methods of discovery," he said.

The ACT senior school system is built on school-based assessments, with no external exams.