The number of students attending private schools in Australia will flatline over the next decade, according to federal government projections, as more parents choose to keep their children in the public system.

Enrolments that were once growing at a rate of 20,000 a year will slow to as little as 3000 by the middle of the next decade, according to the projections, presenting a stark marketing challenge to the nation's private schools.

More parents are projected to keep their children in the public system in the next decade. Credit:Quentin Jones

Public school enrolments will also slow from their current boom, but will still grow faster than they did in the Howard years and up to 2011, a period when private school growth outstripped that of their public counterparts.

Of the 367,000 additional full-time equivalent students projected to be in schools by 2027, it is expected 288,000 - or 78.5 per cent - will be in government schools. At present, 65.6 per cent of the country's children are in the public system, which will inch up to 66.8 per cent by 2027 if the department's projections are accurate.