If I understand you right, this is an app for the teacher, to record attendance of students at each lesson.
Put yourself into the teacher's shoes (or better, interview a few teachers) and think about the entire process:
- What is the teacher's motivation? A requirement by the school? The need to factor attendance into grading? You may identify opportunities for increasing motivation (such as automatic upload into school system, or summary information useful for grading).
- Teacher enters classroom, sees who's there. Does he know the students by name? Does he have to call out every name on the list?
- Are there patterns of attendance? (This is where teacher experience is important!) Is it useful to propose the attendance list from last lesson (or the average attendance), so that only changes need to done?
- How many classes does a teacher have? Is the schedule available in your app, so that you can present the class that is in session right now (without the teacher needing to select it)? Would the teacher want to enter attendance in front of the class (teacher motivations)?
- Do students always sit at the same place (again, teacher experience is needed!)? Would that help for recording (e.g., by representing the place arrangement in the attendance list)?
- Should there be a count of registered students, to check whether all have been registered?
- What about late-comers or early-leavers? Does the teacher have to change attendance information for them? (Maybe there are school regulations what counts as "attended"?)
- What device are you designing for? A list of 30 people is hard to see on a smartphone, but easy to organize on a tablet.
Once you have this information, you're ready to start design.
I guess I would - without all this information, which can only result by chance in a good design - go for a list of students, with a proposal of who's attending, ordered by frequency of attendance (to allow quick skimmming of those who are likely attending today again).
As a note to your swiping idea and Gustav's answer: I think the swiping idea is good since tapping is so easy: It's easy to tap the wrong student, or tap twice (assuming the entry is deselected again). Swiping is easy on the thumb (assuming smartphone!) and allows for simple corrections (teacher sees the wrong student moves, and stops swipe before it's completed).
If you add some more information, we might be able to give more specific advice.