 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.