In large courses with many student groups, instructors may wish to filter SpeedGrader by student groups. When the Launch SpeedGrader Filter by Student Group setting is enabled, you must select a student group when you open SpeedGrader to grade an assignment, quiz, or graded discussion or from the Gradebook. Only students from the selected group will display in SpeedGrader.

Read more about enabling SpeedGrader to launch filtered by student group