I had classes that were 100% required or you fail that were required to graduate. Its a good lesson to be in attendance on-time and prepared when your a teacher.
You get slackers whose sole purpose is to annoy and continue to play sports/meet women/party or all three, but a person will almost always have these distractions around them. A good teacher knows how to handle them (If your a sympathetic teacher, you might even tell them to straighten up once before you throw them out and give them their grade). You'd think that in college, you wouldn't have to ask an adult to not act like a middle-schooler (you don't either, you can return the favor and treat them like one). Sadly, not always the case in undergrad. Grad courses were always a pleasure to attend.