The report Heterogeneity in graduate earnings by socio-economic background measures the average earnings of graduates six months and three-and-a-half years after leaving university.
It suggests that six months after graduating private school alumni earn an average of £21,643 – compared to £18,919 for those who went to state schools. After three-and-a-half years the figures are £28,592 for private school cohorts and £24,044 for state school students.
The report suggests the reason behind the disparity includes the increased opportunities for privately educated students to attend more expensive universities and study subjects such as engineering and economics, that typically lead to higher-paid jobs.
But even after taking away all other factors, the salary difference between private school and state school graduates is still around £1,500 – or 7%.
The report's co-author and IFS research fellow Claire Crawford said that the figures may point to wider trends within social mobility and earning potential.
"These results suggest that there is a pressing need to understand why private schooling confers such an advantage in the labour market, even among similarly achieving graduates, and why higher education does not appear to be the leveller it was hoped to be," she said.
According to the report: "It is perhaps particularly surprising that a ‘private school premium’ exists even among a relatively advantaged sample."
