Educators believe it is the biggest leadership shake-up of the public system in Tasmania's history.

Yesterday, there were 20 top teaching jobs up for grabs on the state government's careers website.

That included primary school principal vacancies at Bracknell, Deloraine, St Leonards, Mole Creek and Westbury, and high school roles at Exeter and Scottsdale.

The Education Department confirmed that 28 principals had been recently appointed, and another 24 would soon be filled.

Tasmanian Principals Association president David Raw said the glut of jobs was partly due to baby boomers retiring and partly because the department had held off on hiring.

``Personally, I think it's fantastic. The next three to four years will be a really exciting time for the profession as we hand over the reins to the new crew,'' Mr Raw said.

He predicted it would take about 18 months to bed down so many senior staffing changes, which he had not witnessed before.

Australian Education Union state president Terry Polglase said the latest round of principal vacancies was just the beginning.

``I expect that at least one in every three schools will end up with a different principal this year, and possibly one in every two,'' he said. ``We knew that 70 per cent of principals were ready to retire within five years. What we have to prepare for is the 70 per cent of teachers who are about to retire.''

Mr Polglase accused the department of holding back on vacancies to try to introduce a new classification system of schools that would save money on salaries.

Education and Skills Minister Nick McKim said the top jobs had become vacant because a large number of principals were switching jobs or retiring.

``The department is endeavouring to have most of these appointments in place for the start of term 3, which will provide stability and certainty for local school communities,'' he said.

``The new principals will be chosen by a rigorous selection process, and will work to enhance their schools and our government school system as a whole.''

In April, another 30 advertisements for principal jobs were posted on the government website.