EXETER, Campbell Town and Cressy high schools are among 28 in rural and regional areas invited by the state government to consider extending to year 11 and 12 from next year.
Education Minister Jeremy Rockliff named the schools as part of the Liberals' plan to lift the state's retention rate to 81.6 per cent by 2015 and 90 per cent in a decade, when all schools will offer the senior years.
The retention rate sits at 67 per cent.
The government will spend $45.5 million over the next four years extending 21 rural and regional schools.
There has been no costing as to the full amount of the 10-year plan.
Stage one in 2015 will see four high schools introduce year 11 and 12, followed by another five in 2016 and six each in 2017 and 2018.
"We are reaffirming our commitment to invest in education, create a job ready generation," Mr Rockliff said.
"We know to give the best chance for our students, our kids, our young people, the best chance of a job, is to invest in education but of course to extend the school years to year 12."
Others have raised concerns about the plan's cost, the required infrastructure, a lack of specialist teachers in the state and too few students to support eight colleges as well as more than 50 high schools.
Opposition education spokeswoman Michelle O'Byrne said the state's college system would suffer. She has called on Mr Rockliff to name the ones he intends to close because "not all can survive if this plan goes ahead", she said.
Greens education spokesman and former education minister Nick McKim raised similar concerns and said Mr Rockliff was pushing ahead with the proposal without any evidence that it would achieve the claims.
Australian Education Union state president Terry Polglase said he welcomed the attention to address retention but the union's concerns remained around the long-term rollout of the policy and its effect on the colleges.