Heterogeneous grouping is great for classroom productivity and culture—provided, of course, it’s well implemented. And successful implementation begins with ensuring all groups reflect the balance in diversity you’re striving for. That’s why you should assign students to groups strategically rather than randomly—and rather than let students choose groups themselves.
Start by identifying the factors for which you want to ensure diversity, then divide students into groups accordingly. If, for example, peer tutoring is a primary function of your groups (as it was for mine), be sure each group has at least one “go-to” person in it, with other students reflecting a range of remediation needs. Other possible factors may include gender, race/ethnicity, behavioral challenges, and attendance (if you teach at a school with high truancy rates, as I did).