Academically able pupils from black Caribbean backgrounds are regularly denied the opportunity to achieve the highest grades in national tests.
While able white British pupils are usually entered for higher-level maths and science tests at the age of 14, black Caribbean pupils with the same record of achievement are not.
Steve Strand, from Warwick University, analysed key stage 3 test data from more than 15,000 14-year-olds. His findings are being presented today at the British Educational Research Association conference in Edinburgh.
The data reveals that for every three white British pupils entered for the higher-tier maths and science exams, only two black Caribbean pupils are entered.
Pupils who are not entered for the higher tiers are unable to achieve the top test scores available at key stage 3, even if they are academically capable.
Dr Strand noted that Pakistani, black African and Bangladeshi teenagers were also under-represented in these higher-tier tests. For these pupils, the decision was based on prior achievement at the age of 11; their KS2 results indicated that they were believed to be academically unsuited to the higher-level tests.
This was not the case with black Caribbean pupils, whose scores at age 11 matched those of their white British counterparts. And the decision was not explained by social factors, such as class, gender, free school meal entitlement or single-parent households.
Dr Strand said: "After accounting for all measured factors, the under- representation is specific to this one ethnic group." He believes some teachers assume that because teenagers misbehave repeatedly they are not academically able.
But Dr Strand also suggests that low teacher expectations - or "institutional racism" - could account for the low attainment of black Caribbean pupils.
John Bangs, head of education for the National Union of Teachers, said: "Obviously, teachers have to be alert for low expectations based on race. But I think he's picked the wrong target.
"There's a fundamental flaw in the notion of tiering. It can embed low expectations. I think all pupils should be able to get all levels."
The Government is considering replacing the existing system with single- level tests. These tests, which are currently being piloted in 10 local authorities, allow teachers to enter pupils for a test once they feel the teenagers are secure at a certain level. At the moment, they must wait until the end of the key stage.
But Dr Strand fears that this may worsen the situation. "Single-level tests will give even greater emphasis to teachers' judgments," he said. "These proposals may need to be reconsidered."