Private schools are another institution used in attempt to narrow the racial achievement gap. A disparity between achievement gaps in private and public schools can be seen using a U.S. Department of Education database to compute the average National Assessment of Educational Progress test score differences between black students and white students in both public and private schools.
White/Black NAEP Achievement Differences for Public and Private Schools shows a sizeable achievement gap between black and white fourth-graders in both public and private schools. However, the private-sector achievement gap is narrower in the 12th grade than the fourth grade for all of the core NAEP subjects. Public schools, on the other hand, see a larger gap in both writing and mathematics at the 12th-grade level than at the fourth. Averaged across subjects, the public school racial achievement gap is virtually unchanged between fourth and 12th grades, while the gap in private schools is an average of 27.5 percentage points smaller in the 12th grade than the fourth.
The achievement gap closes faster in private schools not because white private school students lose ground with respect to white public school students as they move to higher grades, but because black private school students learn at a substantially higher rate than black public school students. Economist Derek Neal has found that black students attending urban private schools are far more likely to complete high school, gain admission to college, and complete college than similar students in urban public schools. Similarly, in a study comparing graduation rates of all Milwaukee public school students (of all income levels) with those of the low-income participants in the city's private school voucher program, Manhattan Institute Senior Fellow Jay Greene found the voucher students were more than one-and-a-half-times as likely to graduate as public school students.
However, others argue that private schools actually perpetuate and exacerbate the achievement gap. Without controlling for student background differences, private schools scored higher than public schools. However, a study showed that demographic differences between students in public and private schools more than account for the relatively high scores of private schools. In fact, after controlling for these differences, the advantageous "private school effect" disappears and even reverses in most cases. Private schools have selective acceptance and a different demographic. Another criticism is that private schools only serve a small percent of the population and therefore cannot make a huge effect on closing the achievement gap