In some rare cases a class is so easy that it's enough just to read in the textbook and take the tests. In that case you shouldn't be taking the class in the first place. Talk to your undergraduate advisor about perhaps skipping it completely. However, usually people skip class because they are busy with a host of other legitimate tasks (working, family, other classes). If that's the case something is going to suffer from neglect, and often it's that course you are taking. You need to rearrange your life in a major way. Mathematics cannot be learned casually. Signing up for a class and paying tuition for it and then not showing up is a waste of your money and your time.
Fine print, your comments, more links, Peter Alfeld, PA1UM