Under the plan, influenced by the ongoing surge in COVID-19 cases, schools will open on schedule on January 31 for children of essential workers and for students considered vulnerable.
Students in reception, years 1, 7, 8 and 12 will then return on February 2 with other years resuming face-to-face learning from February 14.
Students facing the longer delay will learn online for the first two weeks of term one.
Premier Steven Marshall said a range of options was considered but the strong advice from education officials supported the "hybrid" model.
"We know there was always going to be disruptions for the start of term one," Mr Marshall said on Thursday.
"We want to get as many people into the classroom as possible but we've also got to be mindful of making sure it's safe for students, for our staff and, more broadly, the entire state," he said.
"The reality is there were no easy solutions. There was no simple, clear-cut way of doing this.
"This is a solution which gets the balance right."
Mr Marshall said SA did not intend to close schools should there be infections among staff or students.
The changes for the school year came as SA reported another 3669 new COVID-19 infections and four more deaths, two men in their 80s and two women in their 70s.
The latest deaths take the toll since the start of the pandemic to 30 while SA has 32,516 active infections.
SA Health said 225 people were in hospital with the virus, including 26 in intensive care and seven on ventilators.
Also on Thursday, South Australia introduced new rules for close contacts of cases to have rapid antigen tests rather than a PCR swab.
Anyone who tests positive will be required to report the result through an online system, and failure to report could result in a $1000 fine.
Mr Marshall on Wednesday said mandatory reporting was about getting as much real data into the system as possible to help model the likely trajectory of the current outbreak.
That latest modelling is due to be released on Friday.
Close contacts will be provided with two free RATs which they should use on days one and six while isolating.
The tests will initially be provided through one site established in the Adelaide parklands but more locations will follow.
The parklands site has the capacity to handle about 13,000 people a day and quickly attracted a long queue on Thursday.
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