Student collaboration should encourage students to teach one another. Thus, course material is cemented in the teacher's mind, and the student being taught also benefits. It is hoped the taught becomes the teacher at another time on other topics. Before this study, the authors used class time in their flipped classrooms for quizzes, which served as formative assessments, and solving practice problems in informal groups. Many studies have shown the benefit of collaboration between students 1 so the authors hoped to increase the amount of collaboration among students by assigning students to groups and quizzing them in these groups at the end of each week.To test the group quizzing hypothesis, in Spring 2016, the authors conducted a study in two different courses, each having two sections, all taught in flipped mode. One section for each course was the control group. Collaboration was encouraged in the control group, but not formalized. In the study sections, after the middle of the semester, groups were chosen by the instructors. The groups worked as teams on practice problems, and took a group quiz at the end of the week.Groups were changed each week.Assessment was by comparing changes in exam performance between the control and study groups and through a survey.Comments in the survey indicated a change in student attitude when assigned to a group.Students revealed a desire to be supportive in their groups, and said they prepared accordinglyan encouraging result. However, less encouraging, students confessed to preparing less for group