This is the finding of research by Thomas Gall, an assistant professor in the economics department at the University of Bonn, which was presented at the Royal Economic Society's 2012 conference at the University of Cambridge last week.

In recent years, several US states, including California, Texas and Florida, have introduced "top X per cent" laws designed to increase campus diversity.

Examining data from Texas, Professor Gall and his colleagues found that the policies had not increased university diversity, but had instead increased the ethnic mix in high schools.

"High school students game the system by switching to weaker schools just before graduating so that they can be in the top X per cent," explains a summary of the research.

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"This often leads white, middle-class Texans to move to schools with a broader ethnic mix."

The study found that the policy had increased racial diversity in Texan high schools by 3 per cent - 1.5 per cent owing to "strategic behaviour".

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The "top X per cent" policy could therefore be used as a way of increasing diversity in high schools, the paper argues.

Affirmative-action quotas for ethnic-minority students in Texas were phased out following court decisions in the 1990s and replaced by House Bill 588, more commonly known as the "Top 10 Per Cent Rule".

However, the number of minority students on Texan campuses had fallen by a quarter four years after the introduction of the policy, the research reports.

Taken to their "logical extreme", such policies "would lead to maximal high school integration and little or no university integration", the research postulates. However, the actual effect remains small in practice because of the cost of changing schools, it adds.

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david.matthews@tsleducation.com.