When a teacher has more than one obligation scheduled for the same time, those obligations appear as stacked 'cards' on the grid view of the schedule.
If a teacher clicks on Take Attendance, it will bring back all of the obligations that meet at that time to allow the teacher the flexibility to record attendance for all of the sections that they have meeting at that time. This was created this way based on feedback from schools where, for example, there might be a teacher who teaches 4 sections of a course at the same time and there are a handful of kids in each section. With one click they can easily record attendance for all of them at once.
In order to record one section at a time, the teacher actually has to click on that triangle to the right of the attendance button to reveal a menu where they can choose to record attendance individually per section.
Another option is to have the teacher select List View and select take Attendance next to the appropriate class.