The instructional practice of grouping students according to their academic skills. School-based (or between class) grouping, also known as tracking creates entire classrooms with students of similar ability; within-class grouping forms groups of students of similar ability within an individual classroom.
Proponents of ability grouping argue that student achievement is improved when teachers can target instruction to students’ abilities. Teachers are thus able to raise the level of instruction for high achievers and provide more individual instruction for low achievers. Opponents of ability grouping argue that the practice creates and sustains groups of academic elites and low achievers, with high achievers benefiting from advanced tracks while lower achievers are denied equitable access to high-quality education.
For further explanation:
The National Association of School Psychologists present an argument against ability grouping (requires subscription).