One of the most complex aspects of the achievement gap--one that, by and large, is out of the direct control of educational leaders--is the income gap. Broadly defined, the income gap is the standard of living difference between rich and poor, but in the education system, the gap permeates deeply into many dimensions of a student's progression from kindergarten to senior year. This issue, the fourth in a series on the achievement gap, will explore the income gap, the relationship between the income gap and educational achievement, and practices that promise to mitigate its impact. [For the third info brief, "Closing the Gap: Keeping Students in School. The Achievement Gap: Keeping Students in School. Info Brief. Number 46," see ED532703.]