When I took the course, you could miss a total of 3 classes (out of a course total of 35-40). If you missed more than that, you weren't allowed to take the certification test at the end of the course. You can probably work something out with the instructor if they are reasonable, but if you're going to be missing a lot of classes (i.e. you are a student and plan to miss class over vacation) you should consider taking the course at a later time. For legal reasons, you have to have so many hours to achieve a level of certification, and if you don't, that can't be fudged.