Bright students at disadvantaged schools lag at least two years behind their peers from wealthier schools and struggling students from poor backgrounds continue to fall behind with each year of school, a new analysis of NAPLAN data reveals.

The analysis, in a report by public policy think-tank the Grattan Institute, found that the learning gaps between Australian students of different backgrounds are "alarmingly wide" and worsen as students move through school.

Even if students were doing as well in Year 3, those from a disadvantaged background make one to two years less progress than students whose parents have higher levels of education, the report says.

Bright kids in disadvantaged schools suffer the biggest losses, the report says, making 2½ years less progress than students with similar capabilities in more advantaged schools.