In my high school/gymnasium students needed to bring a signed excuse from parents if they missed a class -- even if they were already 18! -- and too many absences would automatically disqualify the course even if you had a good reason, such as being sick. No overseer really needed for persuading students to attend class.
We had to bring in the excuses too. But the harshest penalty was calling in parents once you reach certain threshold. Which may or may not work, depending on your parents attitude. But as long as you skip a class or two a month, there was next to no consequences. Aside from explaining absent marks in your papers to your parents, of course. Which may or may not be easy to remove. Although forging parents' signature may be even easier.
No amount of absence would invalidate the course. But you if miss a test/quiz/project/etc, you automatically get 1 (out of 10). If you bring in a good excuse - of course you can re-do it at later date. If annual average drops bellow 3.5, school jury decides wether you can transfer to next year or not. In final year, < 3.5 would prevent you from taking that specific exam (which may give bonus points at your chosen university). If that exam is mandatory, then you have to repeat the course next year or drop out...
