The $30 million election policy, announced by Education Minister Jeremy Rockliff on Sunday, would require all state high schools to offer grades 11 and 12 in a bid to see more students complete grade 12.

Mr Eslake said Tasmania’s high school retention rate of 73.4 per cent had risen significantly from 67.1 per cent in 2012, but is still well below the national average of 83 per cent.

“I’m in favour of anything that will give Tasmanian students the same opportunity and encouragement to complete year 12 as students in every other state,” he said.

Mr Eslake agreed with opposition education spokeswoman Michelle O’Byrne that the extension policy would likely lead to the eventual closure of Tasmania’s colleges.

However, Mr Eslake said the present system of colleges was not improving retention rates and was no longer suitable for the modern education system.

“There is something wrong with our system – it is not that we don’t spend enough, because Tasmania spends more per full-time students on school education than any other state than WA,” he said.

Opposition education spokeswoman Michelle O’Byrne said the state government’s “one-size fits all” model would not work, calling for a collaborative model instead.

However Mr Rockliff pointed to the number of schools already signing up for grades 11 and 12 as evidence the plan was welcomed by schools and would not impact colleges.

He said it was his “strong expectation” that all schools will extend by 2022, with $6 million budgeted to hire 70 additional high school teachers.

“The partnerships between our colleges and schools has strengthened,” Mr Rockliff said.

“This is about a mature discussion and policy development that has the number one interests at heart, and that is the best opportunity for our students.”

Tasmanian Principals Association president Malcolm Elliott warned there could not be an expectation that high schools offering grades 11 and 12 would provide the same diversity of subjects as colleges, due to fewer teachers being available in high schools.