"Achievement differences" refers to variations or disparities in accomplishments or successes among individuals or groups. It highlights the varying degrees of achievement in different areas or aspects of life. Full definition
We believe that such a chart provides users a more nuanced view of reading achievement differences between schools in states with relatively low minimum standards. (education-consumers.org)
The same holds for class — in fact, achievement differences by family income now equal or exceed those by race. (nationalaffairs.com)
Virtually all subsequent analyses have included measures of family background (education, family structure, and so forth) and have found them to be a significant explanation of achievement differences. (educationnext.org)