Affirmative actions helps disadvantaged student without hindering advantaged students

In this study 5th through 8th grade students were paid based on their performance on a national mathematics exam relative to other competitor students. The researchers observed the use of a study website as students prepare for the exam to evaluate "investment" in the preparation process.

An affirmative action (AA) element was introduced for "disadvantaged" students by reserving prizes for lower grade students who on average have less mathematics training and practice.

The researchers found that the AA policy significantly increased both average time investment and subsequent math
achievement scores for disadvantaged students.

At the same time, they found no evidence that it weakens average human capital investment incentives for advantaged students.  They believe that this is strong evidence that AA can narrow achievement gaps while promoting greater equality of outcomes.