Attendance Roll in the redesigned Check-in now includes a "group by" dropdown at the top of the list of people. The grouping option allows you to group people by age, household, or a custom detail, for example, by Grade or breakout room.
How to add a custom grouping
Go to Check-in > Settings, and in the Label options field, add any "more detail" names you want to "group by." In this example, "Grade" has been added.
After selecting "Group by Grade" in the Attendance Roll, you can see that the list of children is grouped under headings for each Grade.