The South Australian Government has announced it will reduce the zones for Adelaide High School and Adelaide Botanic High School, in a bid to reduce pressure on both institutions.

Key points: Some students living south-west of the CBD will be rezoned

Some students living south-west of the CBD will be rezoned The State Government says the change is needed

The State Government says the change is needed The Opposition has described the lack of consultation as an "absolute disgrace"

The change will mean some students previously zoned to Underdale High School, Plympton International College and Springbank Secondary College will be rezoned back to those schools in 2020.

The announcement was made as part of a $18 million funding boost for capital works at Adelaide High School to increase its capacity to 1,800 students by 2022.

Which suburbs will miss out?

Minister for Education John Gardner said the zoning changes would only impact new enrolments.

A map showing the suburbs removed from the shared zone for both high schools. ( SA Government )

Mr Gardner said students from the suburbs of Hilton and eastern parts of Torrensville and Mile End will be rezoned back to Underdale High School in 2020.

This will also be the case for students previously zoned to Plympton International College in the suburbs of Kurralta Park, Glandore and eastern parts of Richmond and Marleston.

Students in the suburbs of Black Forest and south-western parts of Clarence Park will be rezoned back to Springbank Secondary College.

Mr Gardner said the change would deliver a sustainable solution to enrolment demands under changes made by the former Labor government.

"When the Adelaide Botanic High School came online the previous government had decided to significantly expand the Adelaide High School zone, to include a range of new areas, now I'm not sure what advice that expansion was based on, but some of those areas are identified to return to their original zones next year," he said.

"The methodology for determining that has been based on from those new areas to the zone, if they are closer to their original public school and that is either Underdale, or Plympton or Springbank, and indeed those schools have the capacity then that has determined the decision-making there.

"Even without Year 7 moving into high school in 2022, the existing Adelaide High and Botanic High School zone for the period going ahead was already going to be placing these schools under significant enrolment and capacity pressure."

Labor says the decision is an 'absolute disgrace'

Shadow minister for education Susan Close described the decision to change the shared zone as an "absolute disgrace" and one which would be a shock for parents who had bought into the area.

Opposition minister for education Susan Close has slammed the decision by the State Government. ( ABC News )

"Families who last week had decided where they wanted their kids to go to school, had the plan in place, knew what was happening, suddenly told that overnight, that's no longer the case," she said.

"There are many schools that are full at the moment that will be under threat from an increased enrolment with Year 7, whose zones are also likely to change."

She said the decision was going to have a big impact on families.

"I wonder what's going to happen to real estate prices in the area where parents have bought, understanding that their children will be going to one of these Adelaide city high schools," she said.

"It was always going to be expensive to move an entire year level from primary school to high school.

"Why on earth didn't they properly fund that as part of their election commitments, instead of making families suddenly uncertain about where their kids are going in the future?"

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One Adelaide mother who spoke to the media at Torrensville said the decision would leave parents confused about where to send their children.

"It just confuses people and then people start panicking and they think 'where are we going to take our kids?'" she said.

"They should think of the rest of the population, the people who live around this area because that's what we're used to."

The new Adelaide Botanic High School opened this year. ( Supplied: SA Government )

Another mother in Torrensville said the decision would leave parents with limited options.

"I think that limiting our options only makes it harder and the education system already has enough issues as it is," she said.

The announcement follows the opening of Adelaide Botanic High School, with 350 Year 8 and 9 students starting last month.