- Ability grouping with curricular differentiation comes in many forms and some forms may contribute to the achievement gap more than or differently than others.
- There appears to be considerable evidence that tracking and other kinds of ability grouping with curricular differentiation, extending up to and including grouping at the school level, often contribute to the achievement gap between initially lower- and initially higher-achieving students.
- Student course taking and tracking are the most powerful predictors of academic achievement, far stronger than the effects of either personal background or a wide range of student attitudes and behaviors.
- Differences in the ways that teachers approach their work and the goals they have for classes with students of different initial achievement levels may also help account for the role that tracking plays in increasing the achievement gap.