Premier Steven Marshall has announced South Australian schools will open on January 31 for "all essential children, essential workers, and also vulnerable children".

On February 2, Reception, Year 1, 7, 8 and Year 12 will be able to return to classrooms.

"We know that these are the students with the highest need for face-to-face learning," Mr Marshall said.

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All other cohorts will remain online until February 14.

"We've got an arrangement where other people that need to be in face-to-face learning as of [the] first week will be accommodated," Mr Marshall said.

"There will still be some more information and some discussion regarding the use of Rapid Antigen Tests within that school environment as well as early learning.

"The bulk of our schools plan will be delivered tomorrow."

It comes as the state recorded 3669 new COVID-19 cases and four more deaths.

Two men in their 80s and two women in their 70s passed away, with Premier Steven Marshall giving his condolences to their friends and families.

The number of people with COVID-19 in hospitals has jumped to 225, with 26 people in ICU and seven on ventilators.

Mr Marshall labels free RAT distribution trial 'very successful'

Mr Marshall said today's trial of handing out two free rapid antigen tests (RATs) to close contacts of a positive case was "very successful".

"There are thousands and thousands [of RATs] which have already been distributed," Mr Marshall said.

"The police commissioner tells me this has been very successful with very short waiting time."

The Premier added he was also satisfied wait times at PCR testing sites had reduced, with many he said showing a one or two-hour wait time.

Mr Marshall said there will also be agreements with different councils across the state to set up RAT distribution sites.