Instructors provide more positive, and thus useless, feedback to minority students than to white students:
"The social implications of these results are important; many minority students might not be getting input from instructors that stimulates intellectual growth and fosters achievement," notes Harber. "Some education scholars believe that minorities under-perform because they are insufficiently challenged -- the 'bigotry of lowered expectations,' in popular parlance," he explains. "The JEP study indicates one important way that this insufficient challenge might occur: in positively biased feedback," according to Harber.
It's funny that teachers behave in this extra-favorable manner largely so that others don't accuse them of being biased. If they weren't super nice to blacks or hispanics, then obviously they'd be racist.
Link via Instapundit.