The Research Findings on Ability Grouping Discussed in the Text

The research findings on ability grouping discussed in the text suggest that

A) between-class ability grouping is most beneficial to low-achieving students.
B) within-class ability grouping is not effective for the primary and elementary grades.
C) there is no empirical support for between-class ability grouping.
D) between-class ability grouping works in conjunction with the Joplin Plan.