Complex sentence: In the early grades, retention rates are similar among white Americans, African Americans, and Hispanic Americans, but by high school, the rate is about 15 percentage points higher for African Americans and Hispanics than for whites.
Split into simpler sentences: In the early grades, retention rates are similar among white Americans, African Americans, and Hispanic Americans. By high school, the rate is about 15 percentage points higher for African Americans and Hispanics than for whites.