SA NAPLAN results among lowest in nation

South Australia's substandard NAPLAN results prove schools should have greater autonomy, the state opposition says.

SA students performed below the national average in 17 out of 20 numeracy and literacy testing categories, preliminary NAPLAN results show.

Students in year 3, year 7 and year 9 recorded above-average results in the persuasive writing category.

But numeracy results were among the lowest in the nation across all four age categories.

Opposition Leader Steven Marshall says South Australia should follow the lead of Queensland and Western Australia by signing up to the federal government's independent public schools scheme.

"We've got terrible school autonomy," Mr Marshall told ABC radio on Monday.

"We're not giving school principals and communities and councils the opportunity to affect results at their local school level.

"We're below the national average, we're consistently at the bottom of the league tables and we've got to do something about educating our kids."

Education Minister Jennifer Rankine said the federal government's decision not to proceed with the Gonski funding model had created an uneven playing field for schools in rural and remote areas.

But the minister said it wasn't immediately clear why South Australian students had performed below the national average.

"I don't think anyone can particularly put their finger on why," she told ABC radio.

"The purpose of NAPLAN really is not about a league table of scores, as interesting as that is ... but to identify students who are struggling and get the assistance they need."

The state government had invested in numeracy and literacy coaches at more than 100 SA primary and secondary schools, Ms Rankine said.