Councillors have approved controversial plans to radically transform secondary education in Powys.
Management could be streamlined, schools could merge and sixth forms could close after the council's ruling board backed the major shake-up.
The decision means all 13 high school sites are likely to stay open after concerns that up to six could shut.
Four months of public consultation will begin in January.
The council's decision is strongly opposed by union leaders who fear heavy job losses.
Last week, the local authority said all 13 high school sites in Powys were expected to stay open.
After widespread opposition, council officers recommended that seven or eight schools would operate across 13 sites.
The council's preferred options for pre-16 and sixth form education are a response to falling pupil numbers and the condition of buildings, the council said.
It could mean schools merging and the streamlining of management structures, leading to one head teacher for three schools.
Teaching posts could also be lost through retirement or voluntary redundancies, the council said last week.
The proposals for post-16 schooling included stripping schools of their sixth forms and opening sixth form centres or working in partnership with the county's further education college, Coleg Powys.
There are also plans to reorganise pre-16 Welsh-medium education across three sites.
Newtown councillor Russell George, one of three board members to vote against the plans, said: "I don't think the economic case for change has been made and the savings identified do not justify the risk of changing our school structure.
"It is imperative we do nothing that harms the present provision. If we are to make change to our school structure, there has to be a clear overwhelming case and at the moment it's marginal.
"Not having a full and working sixth form in some communities such as Llanidloes or Llanfyllin would have a detrimental impact on the school and community, one school site could become the poor relation which I don't think is acceptable."
But Powys council rejected that a school without a sixth form would be weakened. It said schools in other counties did not have sixth forms and students moved elsewhere to study when they reached 16.
The council added that post-16 education in Powys was costing approximately £1m more than it received in funding from the Welsh Assembly Government.
The teaching union NASUWT said last week there would be "wholesale dismissal of teachers and support staff" if the planned changes went ahead.
Powys council's board has also voted to make a £220m bid for Welsh Assembly Government cash to help fund a 15-year plan for primary and secondary education.
As part of a £314m investment programme, the authority will have to find £94m of the total investment.