I am fairly sure that students who attend classes (and pay attention!), do better in exams and continuous assessment than those who choose not to come to class. I am very mindful that some students may learn more from an hour in the Library or reading a textbook, than attending one of my classes. Learning styles vary, and a lecture is not suitable for everyone. Many Colleges monitor attendance in an effort to intervene and provide support when a student is recorded as absent after a couple of weeks. This is also an effort to reduce dropout rates, which are strongly linked to lack of attendance.
|Image source: Taft High School
Often I hear that students will use the excuse that they can get the class notes on-line, and that this is the same as attending a lecture. Even one of my longests sets of notes will take a fraction of the time to read when compared to the time taken to go through them in class. I could spend 15 minutes discussing 3 short bullet points that take 10 seconds to read. I know that there are lecturers who do little more than read out detailed notes in a class - even I would skip such a class. Most of us don't do this - and use class time to discuss points, give examples, ask and answer questions. Outside of all this is the act of getting up and going to College and experiencing life as a student.
Perhaps the day will come when all classes will be delivered in the classroom and on-line at the same time - the on-line version being recorded and archived for students to view later. This is better than missing the class. I recall at a conference presentation that a professor in Trinity routinely recorded his classes in engineering and made them available on-line. The technology to do this is easy and has been available for a long time. The professor did not edit the recordings and discarded them at the end of the academic year, and started all over again the next year. Even though his subject changed little from year to year, he still wanted his students to get a recording of the actual class they missed. Admirable dedication I think you'll agree.
From my point of view I of course prefer a fuller class to a near empty one - I feel it leads to a better teaching experience for me. A classroom is about learning AND teaching - neither takes place for a student who is not there. Attendance matters!